Underground Marvels (2019–…): Season 1, Episode 4 - Kingdom of Salt - full transcript
The Wieliczka Salt mine in Poland, some 327 meters deep, where the voids left behind from excavating salt have been transformed into extraordinary spaces, carved by hand.
Narrator: How were these
life-saving shelters from world war ii...
They were an amazing
engineering construction.
Narrator: ...Turned into
life support for the future?
What goes around comes around.
Narrator: In a mine fraught with dangers...
...Why did the miners create
These incredible underground cathedrals?
And what is the amazing
history of the underground world
Hidden behind this castle?
♪
Beneath our feet lie
extraordinary chambers...
Caves, vaults, and tunnels.
The span and the size is just crazy.
Narrator: ...Some designed
and built by humans,
Others formed over thousands of years.
But how were they created and adapted?
By whom and why?
You got to face your fears.
Narrator: Throughout
history, subterranean life
Has captured our imagination.
We're going further and deeper
To unearth the mysteries, the stories,
And the secrets of underground marvels.
Poland lies at the center of europe,
East of germany.
It's home to 38 million people.
Best known now for its
iron and steel industry,
Poland's most famous
historical export was salt,
A mineral once considered
more valuable than gold.
But while many mines could
be dark and haunting places,
How did this one become
such an incredible space
For craftsmanship?
What hazards did the
miners have to overcome...
...To create this world of
wonder carved by hand?
♪
On the outskirts of
krakow in southern poland
Lies the wieliczka salt mine,
An ancient world carved out by humans.
It opened in the 13th century,
And for the next 700 years,
The miners dug down nine
stories to a depth of 1,000 feet.
There are 155 miles of tunnels
And more than 2,000 chambers.
♪
Wieliczka has only recently
been unveiled to the world.
But its story begins
when the earth was cooling
And some of the biggest
mountain ranges were forming.
The wieliczka salt
mine was built to exploit
Rock salt deposits that were created
Around 13 million years ago
When a prehistoric sea evaporated.
Patrycja antoniak is an expert
on the history of the mine.
Hundreds of years ago,
before a mine was built
To process this prehistoric rock salt,
Locals found the mineral
rising to the surface
In pools and lagoons in
the nearby countryside.
♪
What they found is halite,
A crystalline form of sodium chloride,
A mineral that continues to
shape this space even today.
♪
Antoniak: This is a salt
crystal, cubic in form.
Salt crystallizes in cubes
always, and the salt crystals
Are perfect cubes.
Narrator: This lucrative
commodity caused the mine
To grow quickly in the 13th century.
Working in treacherous conditions,
Men used basic hand tools,
Digging into the unknown
for the precious salt.
The mine employed over 300 workers
And produced over
7,000 tons of salt per year.
By the 16th century, the miners
were winching out two-ton blocks
With the help of horses.
At any one time, there would
be 100 horses in the mine.
And as the mine grew, so did
the risks involved in exploring
This enormous subterranean world.
To this day, you can still
see the evidence left behind.
One of the primary threats down
in the mine was methane gas.
When it reaches levels of
more than 5% concentration,
It becomes highly flammable.
The smallest spark
would cause it to ignite.
As a life-saving measure,
miners were issued davy lamps
Beginning in the early 19th century.
They were designed to
prevent the risk of explosion.
The lamp flame burns inside a mesh screen.
The mesh lets in the air
Needed to keep the flame
burning as a light source,
But stops it from igniting
flammable gas in the tunnel.
It was 1825 when they
started using davy lamps.
Narrator: In addition to methane gas,
Another risk to the miners'
safety was, surprisingly, water.
To prevent the risk of
flooding and collapse,
The miners built channels
to divert the water to pools
And lakes deep within the mine.
Without these innovations,
miners wouldn't have been able
To transform this space
Into the underground
masterpiece it is today.
Wood was also used to
support the largest chambers.
Whereas metal would have corroded
In the damp, salty environment,
The wood turned rock hard.
[ wood creaking ]
Roof collapse was a constant threat.
The miners used specific types of timber
Because they would make
cracking sounds under the strain.
Acting is an early warning system.
Eventually, salt lost its control
over the global economy,
And in the 1990s, declining
salt prices forced commercial
Mining here to end.
But its closing allowed for a
rise of tourism to take hold.
And now visitors from all over the world
Can explore the 155 miles of tunnels
And more than 2,000 chambers.
What the miners created in
these chambers is unbelievable.
Kamil broniowski, a chief foreman,
Knows their layout intimately.
Salt was taken out, an
empty space was left behind.
Narrator: And what the miners
would do with the empty space
Would become the stuff of legends,
A breathtaking record
of their time underground,
Transforming the mines forever.
♪
Narrator: The wieliczka salt mines
on the outskirts of krakow, poland,
Hold many secrets and
mirror the history of the nation.
Deep inside the tunnels and chambers,
After hundreds of years of salt mining,
The empty voids were transformed
into extraordinary spaces...
A cathedral, four chapels,
Galleries of statues and
sculptures, all carved from salt
By the miners themselves.
There are 15 chandeliers
throughout the mine.
Their frames are made of wood
And decorated with
strings of pure rock salt.
In a painstaking process,
the sculptors shaped them,
Giving them a beautiful glass-like finish.
The largest and most stunning of all
Is in the chapel of st. Kinga
With 2,500 crystals.
Antoniak: Before a service in the chapel,
A miner would lower a chandelier
on the rope to light candles.
Narrator: The chapels have carvings
which are almost a century old.
This fresco of jesus and his
disciples at the last supper
Took nine years to
carve, from 1936 to 1945,
Inspired by leonardo da
vinci's renaissance painting.
Elsewhere, there are chambers
with carvings of everything
From gnomes to local heroes.
The janowice chamber
has a set piece tableau
Called "the great legend" carved in 1967.
It's the story of a hungarian princess
Who became a local saint.
It's believed princess kinga
Dropped her engagement ring into the mine.
And this relic was later
found inside the first lump
Of salt extracted in wieliczka.
♪
The tradition of carving statues
from rock salt continues today
In the mine's ground-level workshop.
♪
♪
After 700 years of industry and craft,
The miners of wieliczka have left behind
An incredible legacy,
And one of the most beautiful
manmade underground marvels.
♪
London, England.
Over 8 million people call this city home.
Yet beneath these 580 square miles
Lies a hidden network of tunnels...
There were attempts to
make the exact location secret.
Narrator: ...Steel and concrete
layers intended to protect
Against impending doom.
♪
How were these secret underground spaces
Built during a global crisis?
Dixon: So, in less than two
years in the middle of a major war,
They were an amazing
engineering construction.
Narrator: How would city
residents have lived down here?
Dixon: The government had a concern
That it would take away
some of their fighting spirit.
Narrator: For years, these
subterranean structures
Have been left untouched.
Until now.
If the people who built this
could see what it's being
Used for today, I don't
think they'd believe it.
♪
[ air-raid siren blaring ]
Narrator: World war ii changed
the city and people of london forever.
When the british declared
war on germany in 1939,
They couldn't have known the impact
That the six-year conflict would have,
Especially underground.
While most of world war ii
was fought in continental europe
And the pacific, the german air force,
The luftwaffe, brought
death and destruction
To the streets of britain,
Especially in london.
Dixon: Throughout 1940,
The germans bombed many
cities, london in particular.
And the people really
needed shelter from that threat.
Narrator: On the south
side of the capital city,
Subterranean historian martin dixon
Is about to enter an underground world.
That few londoners even know exists.
Dixon: The country was
desperate to find accommodation
To shelter the public.
By 1940, they decided they
needed a radical solution,
And as a consequence, they
built eight deep-level shelters
For the general public.
Each was to house 9,600,
And this, at clapham common,
is the entrance to one of them.
♪
Narrator: Shortly after the war broke out,
From 1940 to 1941,
eight deep-level shelters
Were built underneath london
...four north of the river thames
And four to the south.
Dixon: Partially, with
the idea that post-war
They could be linked together
into an express rail service
Underneath the capital.
Narrator: So how would
these shelters keep people safe
From the constant
threat of the nazi air raids,
And how are these innovative
spaces making an impact today?
♪
Narrator: During world war
ii, london was heavily bombed
By the nazis.
Deep underground shelters
Were built as a lifeline
for the city's residents.
Yet their location was
kept secret from air attack.
So how would residents know
Where to go in case of an emergency?
Like the rest of the subterranean system,
The clapham common
shelter is hiding in plain sight.
Here's the entrance
protected by a solid pillbox,
Because the shaft was
the most vulnerable part
Of the network, topped with
five feet of reinforced concrete.
There were attempts to
make the exact location secret,
I guess to make sure
That they weren't specifically
targeted by german bombing.
But in a sense, having a
secret shelter is pretty pointless
Because you want, you know,
The topside of 80,000 people
to actually know where they are
And be able to efficiently enter.
Narrator: On hearing
london's air-raid sirens,
Thousands of people
would have raced for cover
In these deep tunnels at a moment's notice.
Dixon: People say that
rather than being frightening
To go underground, it was very reassuring,
And when you see the photos of the damage
That came as a result of the blitz,
You can imagine that coming underground
Was actually quite a
comforting place to be.
So in less than two years
in the middle of a major war,
They were an amazing
engineering construction.
Narrator: The shelters lie
100 feet below the surface.
That's twice as deep as
the london underground
Subway system.
And at this level, shelters would be safe
From any conventional bombing.
Narrator: In emergency situations,
People can't always think clearly.
Designed for ease of use,
Each shelter was split into
two levels by a mezzanine floor.
Dixon: To get into the
shelter is almost 200 steps,
And although there's a lift,
that was only really available
For supplies and for catering.
All of the shelterers would have to use
The spiral staircases
to get into the shelter.
Narrator: Getting underground
quickly was a matter of life and death.
These ingenious stairwells
layered two separate staircases
Within the same shaft.
Dixon: Because there are
two levels to try and increase
The speed with which
the shelterers could enter,
There are actually two
spiral staircases interleaved.
This one leads to the lower floor,
And the one above eventually
leads to the upper floor.
Narrator: So how does a city build
an underground system of this scale
In the middle of a national crisis,
One that would live on and
make an impact even today?
Mostly it was hand dug,
done largely by miners
Because they had the skill in excavation.
Narrator: Each shelter
took a year to dig out.
The miners started with two vertical shafts
Which now contain the
stairs, then cross passages,
And finally the main shelter tunnels.
The same technique is used
to build a regular subway station
Just further below ground.
Dixon: For every advance in the shaft
That the miners would insert
One more segment,
therefore protecting themselves
And the structure from collapse.
As it was extended downwards,
These two-foot-wide segments were inserted
To provide stability
for the whole structure.
Narrator: And the building
materials were proven.
The miners used the same
cast-iron construction materials
As the subway network.
Virtually all of the tunnels aligned
With what you might regard as standard
London transport tunnel linings.
And lptb...
London passenger transport board...
Shows that it was a standard
london transport segment
Reused for the emergency wall work.
Narrator: 300 feet inside the shelter,
There are still signs of the
life-saving infrastructure.
Dixon: The total length of each site
Is about 400 meters, 420 meters.
So collectively, taking it
end to end, there was about
A mile of shelter space
within each structure.
Narrator: So how would city
residents have lived down here?
Bunk beds were built along the walls,
Although people were expected
to bring their own bedding.
And then on top of that,
there was the facility for toilets,
For catering, first aid, or
medical post and so on.
Narrator: Given the size of
the clapham common shelter
And the seven other
deep shelters in london,
It's remarkable how invisible
they are to people today.
Dixon: So up above,
we've got the tube train
Rumbling away, and further out,
We've got clapham high street,
which is a busy thoroughfare.
Thousands of people passing and re-passing.
Yet down here is a hidden world.
Narrator: The northern line train
passes overhead every few minutes,
Carrying thousands of
passengers over the shelter.
Dixon: Go right up there
through that brick wall,
That's clapham common tube station.
[ subway tracks rattling ]
Narrator: As construction
began on the shelters in 1940,
The royal air force was slowly
winning the battle of the skies.
The luftwaffe conceded
defeat after losing more
Than double the number
of planes as the british.
Two years later in 1942, when
the shelters were finally ready,
It seemed they might
not be needed after all.
The immediate threat
of the german air attacks
Had reduced somewhat.
The other reason is the government
Still had the concern
That if people went
into this sort of shelter
That they'd develop some form of...
I think they called it
deep shelter mentality,
Meaning that they would
retreat into themselves
And that it would take away
some of their fighting spirit
If you like.
Narrator: But in 1944, just when
londoners thought they might
Have weathered the worst of it,
The nazis unleashed a
new fury upon the city.
These subterranean shelters
became critical once again,
And remain important to this day.
♪
Narrator: During world war ii,
london's underground shelters
Became crucial as germany
Unleashed a devastating
new weapon upon the city.
In June 1944, the germans
launched their attack
Of the v-weapons
First off, the v-1 flying
bomb, or the doodlebug.
Seeing the devastation
That that could
potentially cause to london,
The government did decide to
open the shelters to the public.
Announcer: New deep shelters built
for this emergency were put to use
And saved the lives of thousands of people.
♪
Narrator: Since the war ended,
few uses have been found
For these old deep-level shelters.
But now, part of the clapham commons refuge
Could be mistaken for
the set of a sci-fi movie.
If the people who built this
could see what it's being
Used for today, I don't
think they'd believe it.
Narrator: 50 feet below the subway
line lies an underground marvel
That's being repurposed into
something completely new.
[ chuckles ]
What an amazing
transition from world war ii
To space-age cultivation.
Narrator: The revitalization of
this world war ii air-raid shelter
Could herald the beginning
of a new era in food production.
Growing underground is an urban farm.
It's situated 33 meters
underneath the streets of
Clapham, london.
We use hydroponics, l.E.D.S
To produce microgreens.
Narrator: This installation
is at the forefront
Of an innovative global
trend of underground farming.
Ballard: Initially, we looked
at over-ground spaces,
But the underground
worked really well for us
Because it's an insulated space
And we have 100 foot of soil above us.
We've got a consistent temperature
About 15 degrees year-round.
We can create the optimum
environment for growing.
Narrator: Fresh food, especially produce,
Is in demand all year round,
But produce is highly perishable
And can have a large carbon footprint
Because it's imported by air and road.
This farm is able to deliver directly
To london's food markets
just a few miles away.
This product conventionally
comes in out of season
From places like israel or egypt.
So, it's reducing food miles and pollution
From large vehicles
coming into the capital.
Narrator: This shelter once,
built to protect london's residents
From the threats of war, is
now the future of urban farming.
We power the site entirely
by renewable energy
And we're working
towards carbon neutrality.
Narrator: Other countries
including, the u.S. And china,
Also look for ways to repurpose
Their neglected subterranean spaces,
And for ways to feed their
ever-growing populations.
Ballard: It's phenomenal to
know how much space is available.
Just think about how future cities
Are going to feed and power themselves
With this growing population that we expect
To have an extra 2
billion people on the planet
By the middle of this century.
Narrator: These deep shelters
Were developed through
strategic engineering
And saved the lives
of thousands of citizens
In their time of need.
Today, this shelter looks to
improve the lives of londoners
For many years to come.
There's a lot of locals that
perhaps don't even realize
This big space is underneath them.
♪
Narrator: Slovenia... a mountainous country
Bordered by austria, croatia, and Italy.
Beneath its peaks, this
picturesque landscape is filled
With limestone gorges,
caves, and underground rivers.
For centuries, the slovenians have relied
On this enchanted underground marvel
For protection from the
elements and from invaders.
How does the terrain
continue to be shaped today?
Kariz: Wow.
Narrator: How have locals chartered
these subterranean passages
As means of survival?
Vilhar: In middle ages people
actually thought that cave
Is the portal door of hell.
Narrator: And what are
the underground secrets
Hidden behind this incredible castle
Perched on the mountainside?
Vilhar: The castle was hidden.
The exit right here was
the best hiding place.
♪
♪
Narrator: The caves at
predjama lie at the start
Of a major underground
system and hide many secrets.
They were carved out over
millennia by the river pivka,
And local guide and explorer
Marjan has extensive
knowledge of these chambers.
Here in slovenia, we say
That we have two slovenia's
...one slovenia is on the surface
And other slovenia is under the ground.
Never in my life I'll explore
all the caves in slovenia.
Narrator: Over hundreds of
years, adventurers in slovenia
Have discovered more than 13,000 caves.
And experts believe many
more are yet to be found.
But some of the legends that surround them
Are more truth than fiction.
♪
Narrator: When predjama caves
in slovenia were first explored,
There were many different stories
And legends of devils possessing the caves.
Vilhar: In middle ages,
people actually thought
That cave is the portal door of hell.
Marjan often visits a specific chamber
Known as the black cave.
It alone is nearly two miles in length.
In the 19th century,
Locals discovered it lurking beneath them
When the cave ceiling
collapsed and caused a sinkhole.
Legend has it the cave was originally
A beautiful white calcite
that was stained by soot.
Vilhar: The theory is that
the first cave explorers,
When they entered the cave,
used lanterns, candles, torches,
And all these smoke deposit on formations,
And that's why we can see the black color.
Narrator: The neighboring
cave, the pivka cave,
Is 215 feet below the surface
And takes its name from
the river that created it.
Vilhar: It's five kilometers in length.
This is known as an active cave.
The water is flowing, eroding the rock,
And actually shaping the cave.
Narrator: Beyond the black and pivka caves,
The river which carved them
from the earth disappears
To inaccessible depths at
least 500 feet below ground.
Many untold secrets lie within
these subterranean spaces,
Ones that have inspired
legends for centuries.
And the pivka river continues to edge away
At this subterranean system,
Which local guides
have exclusive access to.
The postojna cave was
formed by the pivka river
Thousands of years ago,
but the fast-flowing water
Gradually carved a new route underneath.
To see the river below,
One must trek far deeper into postojna.
♪
Kariz: Wow.
Narrator: The pivka river races
through these underground caverns
At speeds of up to 25 miles per hour,
Continuing its remarkable work
Of carving out new underground marvels
And secret hiding places.
It is kind of special to see
that the river in the cave
And be so close to it.
When postojna was first
discovered a century ago,
It looked magnificent...
...Packed with hundreds of stalactites,
Just like those in a neighboring cave.
But in the last 100 years,
Most of postojna's stalactites
have been snapped off
And stolen by souvenir hunters,
While graffiti and paint
decimate the precious formations
That had taken millennia to develop.
And it could take many decades for
The stalactites to grow back.
For new ones to form over
these snapped-off stumps,
It will take 250 years per inch.
The most special thing for me
About this caves are these crystals.
Narrator: Crystallization
happens when water seeps through
The limestone, leaving
behind the dissolved calcite.
As the minerals build up on
the ceiling, a stalactite is formed.
Kariz: You point a light,
and it's like it comes to life
With that glittering, with that sparkling.
It's almost like it's not real.
Narrator: And it's this
appreciation by the locals
For this complex cave system
That makes it such a rich part
of slovenian history and lore.
Vilhar: Here in slovenia we have
a long history of cave exploration
Going all the way back of
time of erazem predjamski.
Narrator: The defensive and
strategic value of these caves
Was exploited by slovenia's
most infamous aristocrat,
The knight erazem predjamski,
Best known as erasmus, a robber baron
Who lived in the area
during the 15th century.
He masterfully used the labyrinth of caves
To evade authorities,
And it was in his magnificent
castle that the story begins.
Predjama castle in southwest slovenia
Is the starting point for a
nine-mile subterranean system.
This impenetrable fortress,
which covers the cave mouth,
Is perched on a cliff face 400 feet high.
It is officially the biggest
cave castle in the world.
Narrator: The caves were first fortified
By a medieval religious
order before passing
Into the ownership of
the house of habsburg,
One of the longest-ruling royal
dynasties throughout europe.
♪
The cliffside location was strategically
Positioned along an important trade route
Linking the central european heartlands
With the adriatic sea.
Kariz: One of the inner walls
of the castle is a natural wall.
It's much easier to defend
the castle from just one side.
It's completely hidden as a safe place.
Narrator: As ownership of the stronghold
Exchanged hands over three centuries,
New stages of fortification
were added step by step.
Each improvement introduced extra layers
Of security, protection, and secrecy.
Kariz: The last part of the
castle was added in 16th century.
Every century added something new.
Narrator: The very first castle
On this site was a confined and damp space,
Hardly a comfortable place to live.
When it was rebuilt in the 16th century,
Ingenious craftsmen came up
with a rudimentary cavity wall system
With voids of air between
manmade and natural rock faces.
The air pockets provided thermal
insulation and the double walls
Effectively became a
labyrinth of hidden routes
Leading into the caves.
Kariz: There was a theory
here that people of this castle
Have a system of secret passages
So that they could move from
one part of the castle to the other
Without being seen from outside.
♪
Narrator: But it was the
aristocrat erazem predjamski,
A renowned robber baron, whose exploits
Would make these secret passages legendary.
♪
Narrator: Predjama castle
in south central slovenia
Is the largest cave castle in the world
And is known as the seat of the knight
Erasmus predjamski.
After murdering a family member
of the holy roman emperor,
Erasmus was condemned to death.
But he escaped into the cave
system surrounding his castle,
Which he knew all too well.
Kariz: Eventually, the soldiers
that the emperor sent found him
And began with the siege.
He's going to be very safe here.
Narrator: These secret
passages continue to inspire
Cave explorer marjan vilhar.
Vilhar: We can say that erasmus was kind of
A first cave explorer in slovenia.
They were using candles,
maybe some oil lanterns,
And this was it.
It was a big challenge for him to go out.
It was a kind of revolutionary
At that time for caving.
Narrator: These caves offered
erasmus a lifeline for survival...
A natural supply of fresh water.
Because it drips through the porous rock,
It was safe from
contamination by his assailants.
♪
Kariz: The ingenuity of people
building the place is apparent.
They took advantage of what nature
Was already offering them.
Now, here we can see the channels.
Narrator: Erasmus may have had
A continuous supply of clean water,
But he also needed food.
The knight-errant had a cunning plan
Which depended on the
caverns behind his stronghold.
Narrator: Now marjan retraces
the difficult climb that erasmus
Took by candlelight.
The secret passage is almost vertical
And extends for 140 feet
From the rear of the castle cave
Up to the forest above the cliffs.
The secret route was unknown
to the emperor's soldiers.
Erasmus used it to avoid their siege
While continuing his raids
for food on neighboring towns.
As you can see, the exit is right here
On top of us.
Going up.
He was going towards the valley
Around 15 kilometers from
here for the supplies and food.
Definitely it was not easy
To bring all the supplies
through the narrow passage
All the way to the castle.
The castle was hidden.
The exit right here was really hidden.
So this was a best hiding place.
Narrator: With the castle fully
supplied, he would taunt soldiers
By sending food down to them.
Kariz: They had no idea
that it would be possible
To have a secret passage in a solid rock.
So for them,
According to the legend, a
much more logical explanation
Was that there were some
dark forces on his side.
Narrator: Of course
erasmus wasn't a magician.
Just a devious robber baron
Who ingeniously used
these extraordinary caves
To hide from the holy roman forces.
In a twisted turn of fate,
Erasmus was eventually
betrayed by one of his men.
As the story goes, after a
year of being held hostage
Within his castle,
erasmus's secluded location
Was shared with the holy roman forces,
And while using the bathroom,
He was targeted and killed by cannon fire.
life-saving shelters from world war ii...
They were an amazing
engineering construction.
Narrator: ...Turned into
life support for the future?
What goes around comes around.
Narrator: In a mine fraught with dangers...
...Why did the miners create
These incredible underground cathedrals?
And what is the amazing
history of the underground world
Hidden behind this castle?
♪
Beneath our feet lie
extraordinary chambers...
Caves, vaults, and tunnels.
The span and the size is just crazy.
Narrator: ...Some designed
and built by humans,
Others formed over thousands of years.
But how were they created and adapted?
By whom and why?
You got to face your fears.
Narrator: Throughout
history, subterranean life
Has captured our imagination.
We're going further and deeper
To unearth the mysteries, the stories,
And the secrets of underground marvels.
Poland lies at the center of europe,
East of germany.
It's home to 38 million people.
Best known now for its
iron and steel industry,
Poland's most famous
historical export was salt,
A mineral once considered
more valuable than gold.
But while many mines could
be dark and haunting places,
How did this one become
such an incredible space
For craftsmanship?
What hazards did the
miners have to overcome...
...To create this world of
wonder carved by hand?
♪
On the outskirts of
krakow in southern poland
Lies the wieliczka salt mine,
An ancient world carved out by humans.
It opened in the 13th century,
And for the next 700 years,
The miners dug down nine
stories to a depth of 1,000 feet.
There are 155 miles of tunnels
And more than 2,000 chambers.
♪
Wieliczka has only recently
been unveiled to the world.
But its story begins
when the earth was cooling
And some of the biggest
mountain ranges were forming.
The wieliczka salt
mine was built to exploit
Rock salt deposits that were created
Around 13 million years ago
When a prehistoric sea evaporated.
Patrycja antoniak is an expert
on the history of the mine.
Hundreds of years ago,
before a mine was built
To process this prehistoric rock salt,
Locals found the mineral
rising to the surface
In pools and lagoons in
the nearby countryside.
♪
What they found is halite,
A crystalline form of sodium chloride,
A mineral that continues to
shape this space even today.
♪
Antoniak: This is a salt
crystal, cubic in form.
Salt crystallizes in cubes
always, and the salt crystals
Are perfect cubes.
Narrator: This lucrative
commodity caused the mine
To grow quickly in the 13th century.
Working in treacherous conditions,
Men used basic hand tools,
Digging into the unknown
for the precious salt.
The mine employed over 300 workers
And produced over
7,000 tons of salt per year.
By the 16th century, the miners
were winching out two-ton blocks
With the help of horses.
At any one time, there would
be 100 horses in the mine.
And as the mine grew, so did
the risks involved in exploring
This enormous subterranean world.
To this day, you can still
see the evidence left behind.
One of the primary threats down
in the mine was methane gas.
When it reaches levels of
more than 5% concentration,
It becomes highly flammable.
The smallest spark
would cause it to ignite.
As a life-saving measure,
miners were issued davy lamps
Beginning in the early 19th century.
They were designed to
prevent the risk of explosion.
The lamp flame burns inside a mesh screen.
The mesh lets in the air
Needed to keep the flame
burning as a light source,
But stops it from igniting
flammable gas in the tunnel.
It was 1825 when they
started using davy lamps.
Narrator: In addition to methane gas,
Another risk to the miners'
safety was, surprisingly, water.
To prevent the risk of
flooding and collapse,
The miners built channels
to divert the water to pools
And lakes deep within the mine.
Without these innovations,
miners wouldn't have been able
To transform this space
Into the underground
masterpiece it is today.
Wood was also used to
support the largest chambers.
Whereas metal would have corroded
In the damp, salty environment,
The wood turned rock hard.
[ wood creaking ]
Roof collapse was a constant threat.
The miners used specific types of timber
Because they would make
cracking sounds under the strain.
Acting is an early warning system.
Eventually, salt lost its control
over the global economy,
And in the 1990s, declining
salt prices forced commercial
Mining here to end.
But its closing allowed for a
rise of tourism to take hold.
And now visitors from all over the world
Can explore the 155 miles of tunnels
And more than 2,000 chambers.
What the miners created in
these chambers is unbelievable.
Kamil broniowski, a chief foreman,
Knows their layout intimately.
Salt was taken out, an
empty space was left behind.
Narrator: And what the miners
would do with the empty space
Would become the stuff of legends,
A breathtaking record
of their time underground,
Transforming the mines forever.
♪
Narrator: The wieliczka salt mines
on the outskirts of krakow, poland,
Hold many secrets and
mirror the history of the nation.
Deep inside the tunnels and chambers,
After hundreds of years of salt mining,
The empty voids were transformed
into extraordinary spaces...
A cathedral, four chapels,
Galleries of statues and
sculptures, all carved from salt
By the miners themselves.
There are 15 chandeliers
throughout the mine.
Their frames are made of wood
And decorated with
strings of pure rock salt.
In a painstaking process,
the sculptors shaped them,
Giving them a beautiful glass-like finish.
The largest and most stunning of all
Is in the chapel of st. Kinga
With 2,500 crystals.
Antoniak: Before a service in the chapel,
A miner would lower a chandelier
on the rope to light candles.
Narrator: The chapels have carvings
which are almost a century old.
This fresco of jesus and his
disciples at the last supper
Took nine years to
carve, from 1936 to 1945,
Inspired by leonardo da
vinci's renaissance painting.
Elsewhere, there are chambers
with carvings of everything
From gnomes to local heroes.
The janowice chamber
has a set piece tableau
Called "the great legend" carved in 1967.
It's the story of a hungarian princess
Who became a local saint.
It's believed princess kinga
Dropped her engagement ring into the mine.
And this relic was later
found inside the first lump
Of salt extracted in wieliczka.
♪
The tradition of carving statues
from rock salt continues today
In the mine's ground-level workshop.
♪
♪
After 700 years of industry and craft,
The miners of wieliczka have left behind
An incredible legacy,
And one of the most beautiful
manmade underground marvels.
♪
London, England.
Over 8 million people call this city home.
Yet beneath these 580 square miles
Lies a hidden network of tunnels...
There were attempts to
make the exact location secret.
Narrator: ...Steel and concrete
layers intended to protect
Against impending doom.
♪
How were these secret underground spaces
Built during a global crisis?
Dixon: So, in less than two
years in the middle of a major war,
They were an amazing
engineering construction.
Narrator: How would city
residents have lived down here?
Dixon: The government had a concern
That it would take away
some of their fighting spirit.
Narrator: For years, these
subterranean structures
Have been left untouched.
Until now.
If the people who built this
could see what it's being
Used for today, I don't
think they'd believe it.
♪
[ air-raid siren blaring ]
Narrator: World war ii changed
the city and people of london forever.
When the british declared
war on germany in 1939,
They couldn't have known the impact
That the six-year conflict would have,
Especially underground.
While most of world war ii
was fought in continental europe
And the pacific, the german air force,
The luftwaffe, brought
death and destruction
To the streets of britain,
Especially in london.
Dixon: Throughout 1940,
The germans bombed many
cities, london in particular.
And the people really
needed shelter from that threat.
Narrator: On the south
side of the capital city,
Subterranean historian martin dixon
Is about to enter an underground world.
That few londoners even know exists.
Dixon: The country was
desperate to find accommodation
To shelter the public.
By 1940, they decided they
needed a radical solution,
And as a consequence, they
built eight deep-level shelters
For the general public.
Each was to house 9,600,
And this, at clapham common,
is the entrance to one of them.
♪
Narrator: Shortly after the war broke out,
From 1940 to 1941,
eight deep-level shelters
Were built underneath london
...four north of the river thames
And four to the south.
Dixon: Partially, with
the idea that post-war
They could be linked together
into an express rail service
Underneath the capital.
Narrator: So how would
these shelters keep people safe
From the constant
threat of the nazi air raids,
And how are these innovative
spaces making an impact today?
♪
Narrator: During world war
ii, london was heavily bombed
By the nazis.
Deep underground shelters
Were built as a lifeline
for the city's residents.
Yet their location was
kept secret from air attack.
So how would residents know
Where to go in case of an emergency?
Like the rest of the subterranean system,
The clapham common
shelter is hiding in plain sight.
Here's the entrance
protected by a solid pillbox,
Because the shaft was
the most vulnerable part
Of the network, topped with
five feet of reinforced concrete.
There were attempts to
make the exact location secret,
I guess to make sure
That they weren't specifically
targeted by german bombing.
But in a sense, having a
secret shelter is pretty pointless
Because you want, you know,
The topside of 80,000 people
to actually know where they are
And be able to efficiently enter.
Narrator: On hearing
london's air-raid sirens,
Thousands of people
would have raced for cover
In these deep tunnels at a moment's notice.
Dixon: People say that
rather than being frightening
To go underground, it was very reassuring,
And when you see the photos of the damage
That came as a result of the blitz,
You can imagine that coming underground
Was actually quite a
comforting place to be.
So in less than two years
in the middle of a major war,
They were an amazing
engineering construction.
Narrator: The shelters lie
100 feet below the surface.
That's twice as deep as
the london underground
Subway system.
And at this level, shelters would be safe
From any conventional bombing.
Narrator: In emergency situations,
People can't always think clearly.
Designed for ease of use,
Each shelter was split into
two levels by a mezzanine floor.
Dixon: To get into the
shelter is almost 200 steps,
And although there's a lift,
that was only really available
For supplies and for catering.
All of the shelterers would have to use
The spiral staircases
to get into the shelter.
Narrator: Getting underground
quickly was a matter of life and death.
These ingenious stairwells
layered two separate staircases
Within the same shaft.
Dixon: Because there are
two levels to try and increase
The speed with which
the shelterers could enter,
There are actually two
spiral staircases interleaved.
This one leads to the lower floor,
And the one above eventually
leads to the upper floor.
Narrator: So how does a city build
an underground system of this scale
In the middle of a national crisis,
One that would live on and
make an impact even today?
Mostly it was hand dug,
done largely by miners
Because they had the skill in excavation.
Narrator: Each shelter
took a year to dig out.
The miners started with two vertical shafts
Which now contain the
stairs, then cross passages,
And finally the main shelter tunnels.
The same technique is used
to build a regular subway station
Just further below ground.
Dixon: For every advance in the shaft
That the miners would insert
One more segment,
therefore protecting themselves
And the structure from collapse.
As it was extended downwards,
These two-foot-wide segments were inserted
To provide stability
for the whole structure.
Narrator: And the building
materials were proven.
The miners used the same
cast-iron construction materials
As the subway network.
Virtually all of the tunnels aligned
With what you might regard as standard
London transport tunnel linings.
And lptb...
London passenger transport board...
Shows that it was a standard
london transport segment
Reused for the emergency wall work.
Narrator: 300 feet inside the shelter,
There are still signs of the
life-saving infrastructure.
Dixon: The total length of each site
Is about 400 meters, 420 meters.
So collectively, taking it
end to end, there was about
A mile of shelter space
within each structure.
Narrator: So how would city
residents have lived down here?
Bunk beds were built along the walls,
Although people were expected
to bring their own bedding.
And then on top of that,
there was the facility for toilets,
For catering, first aid, or
medical post and so on.
Narrator: Given the size of
the clapham common shelter
And the seven other
deep shelters in london,
It's remarkable how invisible
they are to people today.
Dixon: So up above,
we've got the tube train
Rumbling away, and further out,
We've got clapham high street,
which is a busy thoroughfare.
Thousands of people passing and re-passing.
Yet down here is a hidden world.
Narrator: The northern line train
passes overhead every few minutes,
Carrying thousands of
passengers over the shelter.
Dixon: Go right up there
through that brick wall,
That's clapham common tube station.
[ subway tracks rattling ]
Narrator: As construction
began on the shelters in 1940,
The royal air force was slowly
winning the battle of the skies.
The luftwaffe conceded
defeat after losing more
Than double the number
of planes as the british.
Two years later in 1942, when
the shelters were finally ready,
It seemed they might
not be needed after all.
The immediate threat
of the german air attacks
Had reduced somewhat.
The other reason is the government
Still had the concern
That if people went
into this sort of shelter
That they'd develop some form of...
I think they called it
deep shelter mentality,
Meaning that they would
retreat into themselves
And that it would take away
some of their fighting spirit
If you like.
Narrator: But in 1944, just when
londoners thought they might
Have weathered the worst of it,
The nazis unleashed a
new fury upon the city.
These subterranean shelters
became critical once again,
And remain important to this day.
♪
Narrator: During world war ii,
london's underground shelters
Became crucial as germany
Unleashed a devastating
new weapon upon the city.
In June 1944, the germans
launched their attack
Of the v-weapons
First off, the v-1 flying
bomb, or the doodlebug.
Seeing the devastation
That that could
potentially cause to london,
The government did decide to
open the shelters to the public.
Announcer: New deep shelters built
for this emergency were put to use
And saved the lives of thousands of people.
♪
Narrator: Since the war ended,
few uses have been found
For these old deep-level shelters.
But now, part of the clapham commons refuge
Could be mistaken for
the set of a sci-fi movie.
If the people who built this
could see what it's being
Used for today, I don't
think they'd believe it.
Narrator: 50 feet below the subway
line lies an underground marvel
That's being repurposed into
something completely new.
[ chuckles ]
What an amazing
transition from world war ii
To space-age cultivation.
Narrator: The revitalization of
this world war ii air-raid shelter
Could herald the beginning
of a new era in food production.
Growing underground is an urban farm.
It's situated 33 meters
underneath the streets of
Clapham, london.
We use hydroponics, l.E.D.S
To produce microgreens.
Narrator: This installation
is at the forefront
Of an innovative global
trend of underground farming.
Ballard: Initially, we looked
at over-ground spaces,
But the underground
worked really well for us
Because it's an insulated space
And we have 100 foot of soil above us.
We've got a consistent temperature
About 15 degrees year-round.
We can create the optimum
environment for growing.
Narrator: Fresh food, especially produce,
Is in demand all year round,
But produce is highly perishable
And can have a large carbon footprint
Because it's imported by air and road.
This farm is able to deliver directly
To london's food markets
just a few miles away.
This product conventionally
comes in out of season
From places like israel or egypt.
So, it's reducing food miles and pollution
From large vehicles
coming into the capital.
Narrator: This shelter once,
built to protect london's residents
From the threats of war, is
now the future of urban farming.
We power the site entirely
by renewable energy
And we're working
towards carbon neutrality.
Narrator: Other countries
including, the u.S. And china,
Also look for ways to repurpose
Their neglected subterranean spaces,
And for ways to feed their
ever-growing populations.
Ballard: It's phenomenal to
know how much space is available.
Just think about how future cities
Are going to feed and power themselves
With this growing population that we expect
To have an extra 2
billion people on the planet
By the middle of this century.
Narrator: These deep shelters
Were developed through
strategic engineering
And saved the lives
of thousands of citizens
In their time of need.
Today, this shelter looks to
improve the lives of londoners
For many years to come.
There's a lot of locals that
perhaps don't even realize
This big space is underneath them.
♪
Narrator: Slovenia... a mountainous country
Bordered by austria, croatia, and Italy.
Beneath its peaks, this
picturesque landscape is filled
With limestone gorges,
caves, and underground rivers.
For centuries, the slovenians have relied
On this enchanted underground marvel
For protection from the
elements and from invaders.
How does the terrain
continue to be shaped today?
Kariz: Wow.
Narrator: How have locals chartered
these subterranean passages
As means of survival?
Vilhar: In middle ages people
actually thought that cave
Is the portal door of hell.
Narrator: And what are
the underground secrets
Hidden behind this incredible castle
Perched on the mountainside?
Vilhar: The castle was hidden.
The exit right here was
the best hiding place.
♪
♪
Narrator: The caves at
predjama lie at the start
Of a major underground
system and hide many secrets.
They were carved out over
millennia by the river pivka,
And local guide and explorer
Marjan has extensive
knowledge of these chambers.
Here in slovenia, we say
That we have two slovenia's
...one slovenia is on the surface
And other slovenia is under the ground.
Never in my life I'll explore
all the caves in slovenia.
Narrator: Over hundreds of
years, adventurers in slovenia
Have discovered more than 13,000 caves.
And experts believe many
more are yet to be found.
But some of the legends that surround them
Are more truth than fiction.
♪
Narrator: When predjama caves
in slovenia were first explored,
There were many different stories
And legends of devils possessing the caves.
Vilhar: In middle ages,
people actually thought
That cave is the portal door of hell.
Marjan often visits a specific chamber
Known as the black cave.
It alone is nearly two miles in length.
In the 19th century,
Locals discovered it lurking beneath them
When the cave ceiling
collapsed and caused a sinkhole.
Legend has it the cave was originally
A beautiful white calcite
that was stained by soot.
Vilhar: The theory is that
the first cave explorers,
When they entered the cave,
used lanterns, candles, torches,
And all these smoke deposit on formations,
And that's why we can see the black color.
Narrator: The neighboring
cave, the pivka cave,
Is 215 feet below the surface
And takes its name from
the river that created it.
Vilhar: It's five kilometers in length.
This is known as an active cave.
The water is flowing, eroding the rock,
And actually shaping the cave.
Narrator: Beyond the black and pivka caves,
The river which carved them
from the earth disappears
To inaccessible depths at
least 500 feet below ground.
Many untold secrets lie within
these subterranean spaces,
Ones that have inspired
legends for centuries.
And the pivka river continues to edge away
At this subterranean system,
Which local guides
have exclusive access to.
The postojna cave was
formed by the pivka river
Thousands of years ago,
but the fast-flowing water
Gradually carved a new route underneath.
To see the river below,
One must trek far deeper into postojna.
♪
Kariz: Wow.
Narrator: The pivka river races
through these underground caverns
At speeds of up to 25 miles per hour,
Continuing its remarkable work
Of carving out new underground marvels
And secret hiding places.
It is kind of special to see
that the river in the cave
And be so close to it.
When postojna was first
discovered a century ago,
It looked magnificent...
...Packed with hundreds of stalactites,
Just like those in a neighboring cave.
But in the last 100 years,
Most of postojna's stalactites
have been snapped off
And stolen by souvenir hunters,
While graffiti and paint
decimate the precious formations
That had taken millennia to develop.
And it could take many decades for
The stalactites to grow back.
For new ones to form over
these snapped-off stumps,
It will take 250 years per inch.
The most special thing for me
About this caves are these crystals.
Narrator: Crystallization
happens when water seeps through
The limestone, leaving
behind the dissolved calcite.
As the minerals build up on
the ceiling, a stalactite is formed.
Kariz: You point a light,
and it's like it comes to life
With that glittering, with that sparkling.
It's almost like it's not real.
Narrator: And it's this
appreciation by the locals
For this complex cave system
That makes it such a rich part
of slovenian history and lore.
Vilhar: Here in slovenia we have
a long history of cave exploration
Going all the way back of
time of erazem predjamski.
Narrator: The defensive and
strategic value of these caves
Was exploited by slovenia's
most infamous aristocrat,
The knight erazem predjamski,
Best known as erasmus, a robber baron
Who lived in the area
during the 15th century.
He masterfully used the labyrinth of caves
To evade authorities,
And it was in his magnificent
castle that the story begins.
Predjama castle in southwest slovenia
Is the starting point for a
nine-mile subterranean system.
This impenetrable fortress,
which covers the cave mouth,
Is perched on a cliff face 400 feet high.
It is officially the biggest
cave castle in the world.
Narrator: The caves were first fortified
By a medieval religious
order before passing
Into the ownership of
the house of habsburg,
One of the longest-ruling royal
dynasties throughout europe.
♪
The cliffside location was strategically
Positioned along an important trade route
Linking the central european heartlands
With the adriatic sea.
Kariz: One of the inner walls
of the castle is a natural wall.
It's much easier to defend
the castle from just one side.
It's completely hidden as a safe place.
Narrator: As ownership of the stronghold
Exchanged hands over three centuries,
New stages of fortification
were added step by step.
Each improvement introduced extra layers
Of security, protection, and secrecy.
Kariz: The last part of the
castle was added in 16th century.
Every century added something new.
Narrator: The very first castle
On this site was a confined and damp space,
Hardly a comfortable place to live.
When it was rebuilt in the 16th century,
Ingenious craftsmen came up
with a rudimentary cavity wall system
With voids of air between
manmade and natural rock faces.
The air pockets provided thermal
insulation and the double walls
Effectively became a
labyrinth of hidden routes
Leading into the caves.
Kariz: There was a theory
here that people of this castle
Have a system of secret passages
So that they could move from
one part of the castle to the other
Without being seen from outside.
♪
Narrator: But it was the
aristocrat erazem predjamski,
A renowned robber baron, whose exploits
Would make these secret passages legendary.
♪
Narrator: Predjama castle
in south central slovenia
Is the largest cave castle in the world
And is known as the seat of the knight
Erasmus predjamski.
After murdering a family member
of the holy roman emperor,
Erasmus was condemned to death.
But he escaped into the cave
system surrounding his castle,
Which he knew all too well.
Kariz: Eventually, the soldiers
that the emperor sent found him
And began with the siege.
He's going to be very safe here.
Narrator: These secret
passages continue to inspire
Cave explorer marjan vilhar.
Vilhar: We can say that erasmus was kind of
A first cave explorer in slovenia.
They were using candles,
maybe some oil lanterns,
And this was it.
It was a big challenge for him to go out.
It was a kind of revolutionary
At that time for caving.
Narrator: These caves offered
erasmus a lifeline for survival...
A natural supply of fresh water.
Because it drips through the porous rock,
It was safe from
contamination by his assailants.
♪
Kariz: The ingenuity of people
building the place is apparent.
They took advantage of what nature
Was already offering them.
Now, here we can see the channels.
Narrator: Erasmus may have had
A continuous supply of clean water,
But he also needed food.
The knight-errant had a cunning plan
Which depended on the
caverns behind his stronghold.
Narrator: Now marjan retraces
the difficult climb that erasmus
Took by candlelight.
The secret passage is almost vertical
And extends for 140 feet
From the rear of the castle cave
Up to the forest above the cliffs.
The secret route was unknown
to the emperor's soldiers.
Erasmus used it to avoid their siege
While continuing his raids
for food on neighboring towns.
As you can see, the exit is right here
On top of us.
Going up.
He was going towards the valley
Around 15 kilometers from
here for the supplies and food.
Definitely it was not easy
To bring all the supplies
through the narrow passage
All the way to the castle.
The castle was hidden.
The exit right here was really hidden.
So this was a best hiding place.
Narrator: With the castle fully
supplied, he would taunt soldiers
By sending food down to them.
Kariz: They had no idea
that it would be possible
To have a secret passage in a solid rock.
So for them,
According to the legend, a
much more logical explanation
Was that there were some
dark forces on his side.
Narrator: Of course
erasmus wasn't a magician.
Just a devious robber baron
Who ingeniously used
these extraordinary caves
To hide from the holy roman forces.
In a twisted turn of fate,
Erasmus was eventually
betrayed by one of his men.
As the story goes, after a
year of being held hostage
Within his castle,
erasmus's secluded location
Was shared with the holy roman forces,
And while using the bathroom,
He was targeted and killed by cannon fire.