Underground Marvels (2019–…): Season 2, Episode 4 - Underground Marvels - full transcript

[narrator] A laboratory
buried nearly a mile

beneath South Dakota,

is at the forefront of
major scientific research.

Why is this subterranean facility
considered a gold mine for researchers?

And coming underground,
we're trying to understand

the deepest mysteries
in the universe today.

[narrator] Hidden under a London suburb,

is a labyrinth of tunnels,

with an incredible story to tell.

How is its purpose morphed
over the past 100 years?

And what legendary covert operation



was conducted here in World War II?

[man] The Germans knew something was here,

he fed them lie after lie.

[narrator] And in Copenhagen,

this vast subterranean space,

helped save the lives of
thousands in the 19th century.

Now, over a 150 years later,

why are people suddenly
lining up to get inside?

[woman] You sail into the darkness,

where nothing can escape,
not even the light can escape.

[narrator] Throughout history,

life underground has
captured our imagination.

It is very frightening but
also very beautiful experience.

[narrator] Now we're taking you further,



and deeper.

There was all kinds of wild
theories about what could be below.

[narrator] To unearth
the mysteries of these...

Underground marvels.

Located 8,000 feet,

under the Black Hills of South Dakota,

scientists are unearthing answers,

to the most fundamental
questions about our existence.

[woman] We're hiding a mile underground,

at this low level.

[narrator] But before this world
leading research laboratory

began investigating the
mysteries of the universe,

It was known as the Homestake mine.

One of the largest goldmines in the world.

This mine was a cutting-edge of its time.

[narrator] What technological
advancements did engineers achieve

over a 125 years ago

that keeps it operating today?

There's a lot of difficult
engineering that goes into creating

a space like this.

[narrator] And how close are scientists

to making an earth-shattering breakthrough?

[digital beeping]

Prospectors once flocked to Lead City,

with their picks and tow

on the hunt for precious metal.

But times changed,

and Lead is now better known
for groundbreaking research

into particle physics.

Its transition from the
Homestake gold mine,

to the Sanford Underground
Research Facility,

or SURF, was rather surprising.

In the 1960s, Dr. Ray Davis,

a chemist from Brookhaven
National Laboratory

identified the mine as the ideal location

to establish his solar neutrino experiment.

Once referred to as ghost particles,

these elusive neutrinos

originate from the sun during
the nuclear fusion process.

Mark Hanhardt

is an experiment support scientist in Lead,

and has followed Davis' research.

[Mark] So, if you were to
take every atom in the universe

so, I'm talking about every atom in
your body, every atom in the world,

every atom in the galaxy
and break them down,

into the protons, the
neutrons, and the electrons,

the number of neutrinos in the universe

would still outnumber
those by a billion to one.

[narrator] The trouble is,

they're almost impossible to detect.

[Mark] The neutrino doesn't
have an electric charge.

It doesn't couple to the
electromagnetic field.

So, it passes through normal matter.

It passes through you and
me, it passes through even...

the mile of rock that we have overhead.

And they're incredibly,
incredibly hard to detect.

[narrator] And the only way to find them

was to go underground.

Ray Davis came up with the brilliant idea,

of coming underground,

to block out cosmic rays,

to study the reactions that take place

inside the sun.

[narrator] By going underground,

Davis was able to avoid
cosmic ray interactions,

that could affect his results.

And that's something
you can't do on the surface,

because the surface is constantly bombarded

with cosmic rays coming from the sun,

from the upper atmosphere,

from intergalactic sources.

Also coming from cell towers, radio towers.

Even human beings put
off a level of radio activity.

They would overwhelm the signals

that we're trying to pick up with
these incredibly sensitive detectors.

So, our entire goal in coming
underground is to escape

all the noises on the surface.

[narrator] When Ray Davis first
started working on his experiment,

Homestake was still an active mine.

Getting down here meant that he had to fit

the schedule of the mine itself.

He had to be down here
when they were blasting in areas

that were not too far away.

[explosion]

[narrator] Davis came up with a
clever way to search for neutrinos,

using a chemical compound

similar to dry cleaning liquid.

Now, we're in the lower Davis cavern.

This is the same space that Ray Davis

started installing his equipment in 1965.

[narrator] Davis set up a large tank

of chlorine-rich liquid,

in the hopes that some of
the neutrinos would interact

with some of the chlorine atoms

and form argon atoms.

By counting the argon atoms,

the number of neutrinos coming
from the sun could be detected.

However, an interesting thing happened

when Davis searched
for those solar neutrinos.

Only about one-third of the
predicted number were detected.

This anomaly became known as

the solar neutrino problem.

Ultimately, Davis' experiment

was considered a major
scientific breakthrough.

And he was awarded the Nobel Prize

for identifying different
flavors or types of neutrinos.

[Mark] His experiment
was incredibly successful.

It introduced one of the
most important and lasting

mysteries in physics.

[narrator] Yet, long before the
scientists made their home here,

the mining industry created
the groundwork for everything

that would eventually become possible.

During the 1870s,

prospectors arrived
ready to make their fortune

at the Black Hills gold rush.

The Homestake mine became

one of the longest enduring gold mines

and oldest gold mine listed on
the New York Stock Exchange.

[narrator] David Vardiman

is a former Homestake miner,

who now works at the Sanford
Underground Research Facility.

Forty-five years ago as a college student,

I went to work for
Homestake Mining Company.

We had just reached the 8,000 foot level,

and my area of responsibility was

the mapping and geologic control

and identifying locations of ore

in the deep underground
for the Homestake mine.

[narrator] But working a mile underground

is no easy feat.

[David] The 8,000 foot level
is a 132 degrees Fahrenheit

rock temperatures.

So, that's a lot of
challenges on ventilation,

hoisting, personnel,

equipment, you name it.

This mine was a cutting-edge of its time.

[narrator] For over 125 years,

miners pulled more than 40
million ounces of gold from the mine.

To the locals,

a seemingly limitless amount of
riches was buried deep in the ground.

Just waiting to be unearthed.

Yet, in 2002, that limit was reached.

And the mine was forced to close
because of high production costs.

But it was not forgotten.

Five years later,

new life was resurfacing at Homestake mine.

But instead of hunting for gold,

advocates for underground science

were determined to shed light

on one of the biggest
mysteries in the universe.

After over a century of
lucrative gold production,

the Homestake mine,

located in South Dakota,

took on a whole new purpose.

In 2007,

the Homestake mine transitioned into

a dedicated subterranean research lab,

called the Sanford
Underground Research Facility

or SURF,

designed to solve some of
the universe's biggest mysteries.

Above ground,

the original mine
infrastructure is still operating

and is currently the main
mode of transportation

in and out of the lab.

When one cage is going down
the other one is coming up.

77,000 pounds worth of weight,

that this hoist mechanism is pulling up.

This is a vintage piece of hoist here.

You will not see these running

other than in museums.

Yet here, it has been rebuilt,

maintained to support science...

cutting-edge science with
1930 vintage technology.

[narrator] Now, a new kind
of mining is taking place.

We're looking to
understand certain properties

of the neutrino that make
them really important to our story

for how we came to be in the universe.

[faint boom]

We're trying to understand
if neutrinos are...

their own anti-particles.

And if they are, that would explain
a big chunk of what's missing

from the current Big Bang Theory.

[narrator] Even though dark matter makes up

nearly 85% of all matter in the universe,

we don't really know much about it.

What we do know is that it exists,

based on the impact it
makes on the universe.

[Mark] We notice things
like gravitational lensing,

which is, uh, areas, uh, in
the universe where we have

intense gravity that actually bends light

according to Einstein's
general theory of relativity.

But we don't see the mass that's
there in order to generate that gravity.

We don't see what's
actually bending the light.

[narrator] Some researchers believe the
leading candidate for a dark matter particle

is a WIMP.

Or, Weakly Interacting
with Massive Particle.

Because WIMPs interact so
weakly with ordinary matter,

they're extremely hard to detect.

Even though we don't know what a WIMP
is exactly, because we've never seen one,

we do know based on the
properties that we've derived from

what dark matter does in the universe,

what that fingerprint should look like.

[narrator] In a series of experiments,

SURF attempted to prove
the existence of WIMPS.

In 2012, they installed the
Large Underground Xenon,

or LUX experiment.

The detector is filled with supercooled
liquid Xenon surrounded by sensors.

The sensors can detect tiny
flashes of light and electrical charges

emitted if a WIMP
collides with a Xenon atom.

The idea is that as dark
matter passes through the Earth,

and it passes through this lab
and it passes through you and me,

and it passes through our detector,

one out of a billion, billion times,

one of those particles is going to interact

with the nucleus of a Xenon atom,

which is the heart of our detector.

[narrator] Unfortunately, after four years,

LUX was unable to detect any WIMPs.

However, its high levels of
insulation, meant it was recognized

as the quietest detector in the world.

We were more sensitive
while we were running

than any other dark matter
experiment on the Earth.

So we didn't see anything.
But we didn't see it better

than anyone's never not seen it before.

[narrator] But SURF didn't give up.

The facility upgraded and
replaced LUX with the LUX Zeppelin.

Or LZ project in 2016,

aiming to identify WIMPs.

[Mark] We've taken all the lessons
we've learned from running LUX

and made it into something so
much more incredibly complex,

so much more bulletproof.

[narrator] For this highly advanced
equipment to work properly,

these machines need to be
cleaned on a molecular level.

[Mark] There's a lot of
stuff that is radioactive

that we could accidentally introduce
to the experiments including dust.

[narrator] HEPA filters purify the
air that comes from the surface.

This ensures that campus
itself is a super clean area.

To keep the researchers from contaminating
the highly sensitive experiments,

they must dress for the occasion.

So this room is a clean room.

Extremely clean environment, hence,
we've sealed ourselves into these suits.

'Cause you're shedding
particles, you're shedding skin,

you're shedding hair, you're shedding dust.

So you wanna keep everything inside,

plus, a mask and a hood

to keep all the particles
that come out when you talk.

[narrator] Research scientist
Cabot-Ann Christofferson

is used to working in
restricted conditions.

We actually do all the
assembly for the experiment

inside the glovebox, which is even cleaner.

[narrator] The particle count
inside a glovebox is typically zero,

creating the cleanest, deepest
underground workspace on Earth.

The conditions are strictly controlled.

[Cabot-Ann] No humidity, no oxygen.

Only nitrogen which, you
know, prevents corrosion.

So, we are hiding a mile underground,

at this low level. Plus, we've
surrounded ourselves with

low radiation concrete.

And then the rock naturally is low
radiation for this area in South Dakota.

[narrator] SURF is now taking part
in the largest neutrino project ever.

DUNE or, Deep Underground
Neutrino Experiment.

It's designed to investigate how neutrinos
automatically change as they travel

becoming a different type of neutrino,

or flavor every few hundred miles.

These will be giant steps for science

and could drastically
revolutionize tomorrow's energy,

environmental, medical,
and industrial processes.

A DUNE is made up of
more than a 1,000 scientists,

spread over more than a
175 different institutions,

in over 60 countries.

Project manager Joshua Willhite

is overseeing construction in South Dakota.

Nearly 800,000 tonnes of rock

will be excavated from
the underground caverns,

making way for a new scientific facility.

Massive machines drill into the rock

and explosives are then
inserted in a specific pattern

calculated by computer.

Heavy blast doors protect the workers

from the powerful explosions
needed to clear the rock.

At Fermilab, outside Chicago,

a new particle accelerator

will send the laboratory's
high-energy beam of neutrinos

800 miles through the Earth
from Illinois to South Dakota.

[Joshua] We are in a sweet spot of distance

from Fermilab to study
neutrino oscillation.

And that's how neutrinos
actually change flavors,

as they travel through time and space.

We're exactly one oscillation,

between flavors away from Fermilab here.

[narrator] Searching for
nearly undetectable particles

requires extremely powerful equipment.

The biggest part is actually
excavating these large caverns.

When I say large, these are...

65 feet wide, 90 feet tall, and almost
500 feet long from the detectors.

And these are unprecedented
at this depth in the world.

[narrator] The neutrinos will
then be intercepted at SURF

by massive vats of super-cooled liquid,

called cryostats.

Once installed,

each of the four giant cryostats

will contain 10,000 tonnes of liquid argon,

which need to be kept
below minus-300 degrees.

Liquid nitrogen will be
used for the cryostats.

But for all the other equipment in the lab,

an enormous ice plant will
be constructed on the surface,

and will produce ice cubes that
are then dropped one mile down,

via a 12-inch pipe.

Once DUNE is fully operational,

the world's scientific
community will be watching.

I think that Ray Davis would
be thrilled at the idea that

what he started in 1965,

has turned into this massive
underground laboratory

for studying the deepest mysteries
that we know of in the universe today.

[narrator] Buried 100 feet
below this quite London suburb,

is a vast subterranean world.

Steeped in both history...

Flint could be sold to gunsmiths

to make muskets and pistols.

...and mystery.

[man] These nine ledges are believed

to being sacrificial alters.

[narrator] How did the tunnels
evolve into one of Britain's

best kept military secrets?

[man] The Germans knew something was here.

He fed them lie after lie.

It groomed to 15,000 people
at the height of the Blitz,

like an underground town.

[narrator] In England, under
a residential neighborhood,

lies an unexpected network of tunnels.

For centuries,

humans have been exploring the depths

of the Chislehurst Caves,

which lie 100 feet below a London suburb.

Stretching 22 miles,

these tunnels and caverns
are entirely man-made,

and were initially constructed
to mine flint deposits

within the London shock lairs.

But for years,

people have been debating their origins.

[Jason] Some people believe

that these tunnels go even
further back to Roman times,

and even the druids.

[narrator] According to legend,

the first phase of the caves

was created by members of the druids,

an ancient Celtic culture.

[Jason] This particular
part of the cave system

is known as the "little
section" or the "Druids' section".

[narrator] In 1903,

one man set out on a quest to
uncover the caves' origin story.

During the Victorian era,

Dr. William Nichols produced
several theories about

who carved out this subterranean space.

Including one that
supported the Druid claim.

[Jason] The Druids are the Celtic people.

They were the lawmakers and givers.

They were the doctors of
sorts, or shaman if you will.

They were a polytheistic religion.
They worshipped many gods.

We're going a long way
back, 3,000, 4,000 years old.

[narrator] Although there are
few written accounts of the Druids,

historians believe their religion
involved the natural world and its powers.

In front of us is a ledge, and it's one
of nine ledges in Chislehurst Caves.

These nine ledges are believed to have
been sacrificial alters used by the Druids.

But this ninth alter,

this is where Dr. Nichols believes
human sacrifice took place.

[narrator] Another one of Dr. Nichols'
theories was that the extensive mine tunnels

could also have been built by the Romans.

[Jason] This painting depicts
how Dr. William Nichols believed

that the Romans removed
chalk in the ancient times.

[narrator] Dr. Nichols' claims
generated a lot of public debate,

and soon the caves drew in
many curious Victorian tourists,

looking for evidence.

People used to come down
here, looking for Roman remains.

[narrator] But the reality turned out to be

quite different from Dr. Nichols' tales.

The first mention of the Chislehurst
caves was found in medieval documents,

dating to the middle of the 13th century.

The charter mentions that the
caves were mined for chalk and flint.

We're on the earliest sets of
tunnels left from the ancient mining.

[narrator] Archeologist Rod
LeGear is an expert on the history

of this subterranean world and its geology.

Chalk is comprised of millions
and millions and millions

of tiny, tiny fossilized sea creatures.

They die, went to the bottom of the sea,

and slowly built up this sludge,

which eventually solidified, became chalk.

[narrator] LeGear has
studied the style of excavation

and the markings on the chalk walls,

to accurately date them.

At some points, while
the mine was being dug,

somebody left their mark on the walls here.

They're dates from 1727 and 1737.

[narrator] He's been cautious not to
misinterpret the origins of the tunnels.

Like the more sensational Dr. Nichols.

Now graffiti's a bit difficult because

you can put anything
on the wall at any time.

For instance, in one part of
the mine somebody has found

"1066, William," which
is perhaps a little dubious.

But the style of the letters here
is about correct for that time.

The simple hand tools...

You can see where the
mark's been left by the miner,

using the pick here and
pulling away the chalk.

Much wider at the base than
the normal picks that we get today.

One of the things that you can date
the tunnels with, is the pick marks.

[narrator] Excavating chalk required an
advanced level of engineering expertise.

Chalk is relatively soft, quite easy
to dig. That leaves some problems.

If you're not careful, if
you don't dig it properly,

the roof is liable to fall in on you.

This is a bad idea.

[narrator] These early
miners had a foolproof plan.

[Rod] Towards the
roof, the wall is arched in

to take the load off the roof.

The bottom, it also arches in,
which gives a very strong profile.

So the roof stays up.

[narrator] While Dr. Nichols'
writings from the Victorian era

describe the chalk platforms
as serving mystical purposes,

Rod believes they were far more functional.

[Rod] He said that these
platforms were Druid's alters.

They have a much
more practical application.

If you imagine that I'm an old miner,

with a pick axe in my
hand, I cannot reach the roof.

A miner would be on the platform,
where he could cut away with his pick,

then cut the bench back two
or three meters, almost leaving

a space to stand on inside the
tunnel that could be driven forward.

[narrator] The chalk that was extracted
from this system of underground tunnels,

had two very distinct uses.

The earliest reason man
dug chalk out of the ground...

was for agriculture.

Just the subsoil was acidic, then
an application of crushed chalk on it,

which is alkaline, combat
the acid, and crops grow better.

[narrator] By the 1700s, a new
use for chalk had been found,

and demand was growing fast.

It was used for building, like lime mortar.

Before the days you could buy
cement, you had to make your own

by mixing lime, sand, et
cetera, to make lime mortar.

[narrator] From the 1700s, much
of the local suburbs of London

were built with chalk from Chislehurst.

Miners also found another
resource buried within the cave walls.

[Rod] You'll notice large bands of flint,

these black lumps which are in the wall.

The miners, initially they
were a pain in the bum,

because when you hit them, they
shattered and sent off sharp bits out.

[narrator] However, the resourceful miners

found a profitable use for the flint.

They could be sold to
gunsmiths to make gun flints,

the old muskets and
pistols in the 17-1800s.

[narrator] By the early 20th century,
the tunnels took on a completely new role

and embraced a covert way of life.

[Jason] He worked for
the UK government, MI5.

Every single thing he told
the Germans, was a lie.

[narrator] When World
War II broke out in 1939,

locals burrowed into the Chislehurst Caves
and used them as an emergency shelter.

Including the family of the
current owner, Jim Gardner.

The public took over and
set up home down here.

Some of the caves were totally furnished to
double beds and wardrobes and chest drawers.

[narrator] For over eight months,

nearly 15,000 people from East London,

made the caves their home.

As the German Air force
dropped bombs from above,

the residents were building
an entire city below the ground.

By the peak of the Blitz,
the caves had electricity,

running water, and an
air ventilation system.

There was also a fully
operational hospital.

[Jim] There was a fear that when large
number of people concentrated underground,

that there would be contagious
diseases and severe illness.

But there were no serious diseases,
no serious outbreaks of anything.

[narrator] Soon Chislehurst
contained so many amenities,

the tunnel became known
as the Chislehurst Hotel.

[Jim] This was the
largest of four canteens,

which were operated throughout the wall.

Tea then was almost sacred.

A hot cup of tea was the
answer to everybody's problems.

There were shops built, a
library, church, various offices.

[narrator] There was also a system
for identifying potential attacks.

[Jim] At the main entrance,
there was a big sign

colored green, amber, and red.

And if it was green, then
fine, you could go in and out.

If it was amber, there was a possibility
of an air raid just about to commence.

And if it was red, nobody went out.

[narrator] During the final
stages of World War II,

Chislehurst Caves played their
most covert and famous role to date,

when a Spanish spy
served as a double agent.

Juan Pujol Garcia, codenamed GARBO,
made history when he orchestrated

one of the most successful
operations against Nazi Germany.

He worked for the UK government, MI5,

but every single thing he told the Germans,

was a lie.

[narrator] Previously during World War I,
munitions from the nearby village arsenal

were stored at the Chislehurst Caves.

By World War II, they no
longer served that purpose.

But nevertheless, GARBO planted
this lie with the Nazis to deceive them.

The Germans knew something
was here because of World War I.

GARBO used that same story in World War II,

to misdirect them.

[narrator] The true genius
of GARBO's lie was that

the caves couldn't be
detected from above ground.

So the Germans never really knew
where the alleged weapons were stored,

which kept the subterranean
refugees safe from harm.

[Jason] You can't see any
of this from an aerial view.

Where would the Germans bomb?

They had no idea where
it was, how large it was,

how many tunnels they were,
or where they actually went.

[narrator] Several major victories
were due to GARBO's success

as a double agent.

The first of these was the Operation
Torch landings in North Africa.

On November 8th, 1942, the
Allied forces planned to invade,

with Dwight D. Eisenhower
as Supreme commander.

Prior to the mission,
GARBO sent a coded letter

through the mail to German intelligence,

with all the details of the operation.

However, he cleverly sent it out,

knowing it would arrive after
the operation was completed.

[Jason] And it built his
credibility with the Germans.

And the Germans would
believe just about anything.

[narrator] He even fooled
them about the D-Day landings.

When he told them that D-Day was
actually happening in a different place,

along the coast of
France, they believed him.

[man on radio] This is the day for
which we people long have waited.

This is D-Day.

[narrator] By the 1960s, the
caves evolved once again,

from a secret military bunker
into an unlikely concert venue.

[Jason] Rock bands started to perform.

Like The Who, The Yardbirds,
The Kinks, Jimi Hendrix,

David Bowie, Mick Jagger, and The Stones.

Some of the names of the
bands are on the walls here.

We've got T. Rex on this side, on the other
side we've got Toto, we've got The Troggs,

a piece of rock 'n' roll history.

[narrator] Today the colorful history of
Chislehurst Caves is still very much alive.

Who knows what the future may hold for
this legendary subterranean tunnel system.

The best may still be yet to come.

[narrator] Concealed beneath the
streets of Copenhagen, Denmark,

lies a shadowy underground world.

When you throw into the
darkness here, it creates sort of

very frightening but also
very beautiful experience.

[narrator] This massive
subterranean network helped

bring an end to a devastating
epidemic that threatened the city.

Copenhagen was a
timebomb waiting to happen.

[narrator] Yet today, these cryptic spaces

have taken on a completely new function.

It was full of water until about 40
years ago when somebody remembered

that these systems were here.

[narrator] What techniques did
engineers use over a century ago,

that allowed the caverns
to stand the test of time?

And what amazing scientific
discoveries were recently unearthed here?

It's quite strange to think
that a beautiful place like this

was never intended for anyone to see.

[narrator] In Denmark, located deep
beneath Copenhagen's bustling city streets,

is a massive subterranean
cavern, hidden from daylight.

Today, over a million people
call this vibrant city, home.

But, in the 1800s, Copenhagen
looked a lot different.

Copenhagen was more like a medieval town
than a city, on the verge of modernity.

It was a time bomb, waiting to happen.

Infrastructure was extremely poor.

The sewers were just small
canals in the sides of the streets.

[narrator] Thomas Riis Jensen is
an expert on the history of this site.

In the 1850s, around 150,000
people lived in Copenhagen.

And they all lived inside
the old fortification system,

approximately, two square miles.

[narrator] Before this underground
space was modernized,

Copenhagen had some major water problems.

[Jensen] Clean drinking water was pumped
in from the lakes, surrounding Copenhagen,

just a few 100 meters away.

Human waste along with animal
waste, and even industrial waste,

would all be gathered in these
open sewers, and just... flow away.

[narrator] The 19th century water
systems were leaking into each other.

Drinking water into waste water,

and waste water
contaminating the drinking water.

By 1853, with the water heavily polluted,

a catastrophic epidemic claimed the lives

of more than 4,700 residents.

[Jensen] Cholera disease
had spread throughout Europe.

It reached Copenhagen during the
summer month, when it was at the warmest.

And you can imagine the smells in the city.

[narrator] The epidemic spread like
wildfire across the densely packed city.

[Jensen] Throughout
just a couple of months,

almost 5,000 people died in Copenhagen.

If you compare it to the
population of the time,

150,000 people.

That is about 1 out of 30
people, a really high death rate.

[narrator] The city needed to
come up with a plan to create

a new drinking water system.

And fast.

So, a decision was made to build a
network of underground reservoirs,

large enough to store clean water.

The entire system of water infrastructure

in Copenhagen was built in only two years,

between the years of 1856 to 1858.

The Cisterns would provide
drinking water for up to two days,

and for the entire city of
Copenhagen back then.

[narrator] Originally, the reservoir
was an open pool of water.

But, to minimize the chances
of pollution and infection,

engineers decided to make
a few upgrades in 1889.

[Jensen] The place consists
of three equally large spaces.

The columns down here, all 280 of them,

are built with bricks.

Between them, you have these
massive arches, and then on top of that,

the roof above us is a concrete cast...

with a capacity of up to
4 million gallons of water.

It's quite a big mystery, why
the place was built the way it was.

When we have engineers visiting us today,

they say that the structure is way
too strong than what it needed to be.

We have to keep in mind
though that the techniques used

were fairly new, when
the structure was built.

So, I guess they would
rather be safe than sorry.

[narrator] Due in part to the skills
implemented by the Cisterns engineers,

the cholera outbreak
was stopped in its tracks.

From the 1850s, cholera was
never a problem in Copenhagen.

So, the cisterns and
the greater infrastructure

of water had proved itself to work.

[narrator] By the 20th century,
as new water purification

techniques developed, and modern
water storage facilities were built,

the vast underground
cisterns were no longer needed.

That's when this space began
to take on a life of its own.

It creates, sort of, very frightening
but also, very beautiful experience.

[narrator] By 1933, the city of Copenhagen,

stopped using their
once lifesaving cisterns.

And in 1981, they were
drained and abandoned.

Fifteen years later, the cisterns quenched

a new thirst for scientific exploration.

[Rosing] I've, actually,
vividly remember seeing

the first photo that was in a newspaper,

when somebody remembered that these
cisterns were here and reopened them

and bought up these photos of
this absolutely amazing structures.

[narrator] Professor
Minik Rosing is a geologist

at Copenhagen University,

and perhaps, an unlikely
advocate for this underground layer.

It's a wonderful place because we
don't have such places in Denmark at all.

[narrator] Given its flat
terrain and proximity to water,

Denmark isn't commonly known
for its geological discoveries.

But when the Cisternerne was
converted into a museum in 1996,

a remarkable find was made.

And soon geologists
started paying attention.

It was full of water
until about 40 years ago,

when it was emptied and...

It's beautiful because it's
a piece of almost geology.

[narrator] Stalagmites and
stalactites have begun forming here,

just like they do in
caves, around the world.

But here, the timeline
for growth is much faster.

[Rosing] You know, when the water was

drained out of the cisterns, and...

These things could not have
formed when they're full of water.

You can see, one of these things is

almost like a tree, upside down.

And inside, it'll have a
structure like tree rings.

So, if it's put under microscope,

you'll see layers formed
through these past 40 years.

[narrator] And it's not just
geologists who are experiencing

the perks of this cavernous world.

[La Cour] This is not a place that
an art curator would normally work.

[narrator] Astrid la Cour is
a curator at the Cisternerne.

She's seen firsthand the ups and downs,

this environment has on the art.

Well, to work here is a
challenge to put it mildly.

Um, it's not at all what you think
of, as a normal art gallery space.

Normally you work with white walls
and a lot of light, and climate control.

Down here, you have
humidity just below 100%,

and there's no daylight.

[narrator] Despite the unusual
setting, many artists have created

inspired art installations,

using the unique
atmosphere as their canvas.

Tomas Saraceno, an Argentinian artist

responsible for the latest exhibition,

has taken that to heart
in a way, that has changed

even how guests move through this space.

This exhibition is very different
from other art exhibitions,

'cause you have to
experience this from a boat.

You sail into the darkness,

and the title of the
exhibition is "Event Horizon",

which is the rim of the
blackholes in the universe,

where nothing can escape.
Not even the light can escape.

It creates, sort of, very frightening
but also, very beautiful experience.

[narrator] This installation required
the reflooding of the cisterns.

And what was revealed
afterward was unlike anything

Professor Rosing had seen before.

[Rosing] Water that's standing
here is rich in carbon dioxide.

And the water coming
from below is rich in calcium.

And these two things have
basically made, they loved their life,

and formed the limestone, when they met.

[narrator] The new formations
called helictites are rare calcifications,

similar to those on the ceilings
and floors of the cisterns.

Geology has one fundamental
rule that will let us guide by,

and that would say, "the
present is the key to the past".

So, to understand things that
happened in Earth's past history,

we have seen them unfold
themselves in the present.

[narrator] Whether through artistic
creation or scientific observation,

the Cisterns continue to broaden
the minds of all those who visit.