As water seeks its level, it becomes acidic.

And when it flows over limestone, it etches a path into the rock.

Given eons of time, water will burrow and carve,

with incredible force, the veins and arteries of planet Earth

So the underworld of caves is born.

And after torrents have done their work,

patient drops do more wonders in a million years or so.

Look now on a landscape no one dreamed existed just a few years ago.

Here are bizarre and fantastic treasures that stun the eye

and strain the imagination.

Here is discovery and danger.

Here is adventure.

In New Mexico, members of a National Geographic Society expedition

explore the world's newest and most exotic major cave.

They are following one of man's most ancient imperatives

to see and understand the unknown.

Join us now as we embark on

an extraordinary journey deep into the earth

to confront MYSTERIES UNDERGROUND.

In the Guadalupe Mountains of southern New Mexico,

an awesome giant has lain hidden for a million years.

Sometimes, in the desert silence,

the monster could be heard breathing.

The sound came from a yawning chasm in the rocks.

In 1986 a trio of weekend explorers broke through a layer of rubble

and discovered a new cave only a few miles

from famous Carlsbad Cavern.

Although the cave entrance lay inside Carlsbad Caverns National Park,

park officials allowed qualified cavers to explore it.

One of them was Rick Bridges, an oil and gas prospector.

Now Bridges leads a hand-picked team of experts,

like rock climber Dave Jones, on the 25th expedition to Lechuguilla.

You got the survey gear, Anne?

Research geologist kiym Cunningham

will handle the science studies for the expedition.

Nuclear test engineer Anne Strait is an expert

in surveying and mapping caves.

And specialist cameraman from England, Sid Perou,

will be the first to document Lechuguilla on motion picture film.

The journey begins with a deceptively ordinary hike.

The cave is named after a desert plant that grows in this harsh,

dry environment-Lechuguilla-Spanish for little lettuce.

Forty people will support the venture,

including two support teams to pack in supplies

and batteries for photographic lights.

On high rope.

We tend to have this feeling that

the surface of the earth is the life of the earth.

But we're just this small,

thin little shell that we choose to call our world,

and beneath it there's an entire realm that we know very little about.

And we can, if we choose,

enter that realm and we can learn something from it.

I will never go to the moon,

but I can go to a cave the nobody else has been to

and have the same elation of exploration in the sense

that I have gone where no one's gone before.

Bombs away.

I would like to think that had I lived in another time

I would have been an explorer.

You know, had I lived in the late 1700s,

I would have wanted to know what was across the Appalachian Mountains.

If I'd been around when Lewis and Clark went to the coast,

I'd liked to have gone with them, you know.

And I think most people that cave

at this level and do this kind of exploration feel that way.

Here, Bridges and his companions

excavated to break into Lechuguilla for the first time.

Now the entrance is protected by a lockable hatchway.

Through this tiny aperture the cave breathes

blowing air out or sucking

it in to equalize with the barometric pressure above ground.

Winds up to 60 miles an hour howl out of here,

hinting at the vast underworld below.

Today, this is Lechuguilla's only known entrance,

and there may have never been another.

For a million years this place has lain undisturbed.

In a real sense, it is a primordial world,

untouched by all but microscopic forms of life.

On rope!

It's a long ways down.

See you guys on the bottom.

Dave Jones starts down

the 150 foot pit called Boulder Falls

It was here that the first explorers realized

what a vast place they had discovered.

As you progress down,

it gets steeper and steeper and pretty soon you're free hanging,

but your feet are still against the rock

And all of a sudden you rappel

by this little ledge

and there's no more rock. There's nothing in any direction.

Beyond the base of the pit

the cave branches off in all directions.

Only computer imagery can portray this labyrinth.

After the May 1986 exploration

the cave was known to be 700 feet deep

and more than half a mile long.

Today the system totals 60 miles and plummets more than 1,600 feet.

Twisting capillaries and veins pierce the earth in all directions.

This is a gigantic maze in three dimensions,

defying conventional ideas of direction and scale.

Footprints remain forever in this fragile environment.

Plastic ribbons keep cavers on main trails.

Expeditions into Lechuguilla have been likened to exploring Everest

only in reverse.

The team is headed for Base Camp still hours away.

The trail leads on into inky blackness

Often they traverse chambers so vast

the cave walls are barely discernible.

Gypsum crystals sparkle along the route.

Now, cavers encounter Lechuguilla's fantastic decorations

for the first time.

Helictites and gypsum flowers extrude from the walls

fragile gardens that have taken centuries to blossom,

as minerals have been squeezed from the rocks like toothpaste from a tube.

Beauty abounds.

These jewels of the underground

are exquisitely delicate needles of selenite.

With the constant maneuvering up down

and through the cave's difficult terrain,

50 pound backpacks become painful burdens.

Always, in Lechuguills, danger is not far away.

Okay, on three. One, two, three.

In 1991 seasoned caver Emily Mobley slipped and broke her leg

while working on a surveying expedition in the cave's western sector.

A mile and a half from the entrance,

900 feet below the surface,

this accident would trigger the largest and most publicized cave rescue

in U.S. History.

A hundred experienced cavers

summoned to the scene would labor four arduous days

to bring her to safety.

The bond of comradeship that unites

the caving community was seldommore evident than during this emergency.

Every caver knows and instinctively responds to the code of the underground

that only cavers can save and protect each other.

After almost four hours, the expedition reaches Lake Lebarge,

the first sizeable body of water to be discovered inthis branch of Lechuguilla.

Beautiful!

One of the greatest sights in caving, isn't it?

Yes. Fantastic. Is this Lake Lebarge?

Yeah. Lebarge Borehole looks easier now.

Beautiful!

On rope!

The lake completely blocks the way ahead.

Cavers had to wade it until they found a detour

tricky, but possible.

Well, I think of particular moves like dancing around the edge of Lebarge

as almost a ballet, an underground ballet.

I know where my footholds are; I know where my handholds are.

I know if I hit them just right and move just right

some of them are kind of dynamic in so much as you leave one handhold

while you're going for the next foothold.

And if you do that just right and you have your pack balanced

just right, you flow through it real smoothly.

And so I think it's very much like doing a dance,

a very intricate dance.

And you want to do it perfectly,

you know, and it's very beautiful when you do.

Deeper into the cave,

mineral formations become more fantastic and delicate.

Cavers must move among them with great care.

Spikes of aragonite,

one form of calcium carbonate, grow in fragile bushes.

The gentlest touch could damage them.

There is infinite contrast here.

The now famous Chandelier Ballroom is one of caving's classic beauty spots

Plumes of gypsum sprout from the ceiling,

some as long as 20 feet

the most dazzing examples of their type ever found.

Utter silence pervades Lechuguilla.

The only sound is made by the intruder

In the constant 68-degree temperature and high humidity,

dehydration is always a threat.

Anybody else need any hot water?

For some, the notion of life

with almost a quarter mile of rock overhead

can be oppressive, even terrifying.

But cavers like Bridges relish the experience.

It's almost like coming back to home after you've been gone for a while.

It's a very comfortable feeling to me, particularly in that particular cave.

And you know it's a sense of isolation

The world becomes very simple

Here there is no day or night.

If they ignore the time, cavers tend to stay awake,

and sleep, for longer and longer periods.

In Lechuguilla Cave,

there is little evidence of life.

But this is rare.

Many caves harbor a hidden kingdom of creatures, dominated by bats.

Bats thrive in darkness.

They navigate not by sight,

but by subtle patterns of reflected sound.

Some caves are home to millions of bats,

the greatest concentration of mammals anywhere.

Their nitrogen-rich droppings, or guano,

are harvested as a fertilizer.

Large deposits produce a toxic gas, which can be lethal.

Mountains of bat guano support the intricate food chain underground.

Sometimes, an injured bat, or a baby,

falls into the guano and itself becomes food.

Within minutes the bat is reduced to a skeleton.

Abundant underground, the cave cricket

Crickets spend much of their time gathering food outside their caves,

but inside they perform a vital role as scavengers.

In mute testament to their environment fish have evolved here without eyes.

The salamander has dispensed with eyes, too,

and has no need of skin pigment in a world without sunlight.

People have probably always found shelter in aves.

Thousands of years ago,

as much of the world still lay in the grip of the last Ice Age,

prehistoric hunters left spectacular evidence behind them.

The human spirit was born and nurtured here,

its expression etched on walls of stone.

By the early 20th century most people lived elsewhere.

But science and curiosity drove some to explore deeper underground.

Magnesium flares lit the way, filling dark voids with light.

Geologists squeezed into subterranean chambers

seeking to understand their origin and structure.

And soon the ancient lure of caves turned to profit.

Tourists went underground.

Then and now,

humans have been compelled to seek out caves,

and to combat the gloom with gay defiance.

In the United States, New Mexico's Carlsbad Caverns

was declared a national park in 1930.

But natural wonders were not enough.

Carlsbad and other caves promoted all sorts of attractions,

some a bit farfetched.

The time will come when some master musician

in the Carlsbad Cavern will be able to create s symphony in stone

Many parts of the world are known for caves.

Because most lie on limestone bedrock,

the soil is often thin and life is hard

So it has often been in the remote uplands of Kentucky.

But the automobile brought a new source of wealth

city folks, eager for amusement.

Everyone who owned a cave hung up a sign.

Each was touted as being bigger and better than the others.

The so-called Cave Wars spurred bitter feuds and even violence

Crystal Cave belonged to the Collins family,

but it was too far from the beaten path to prosper.

Thirty-seven-year-old Floyd, one of the Collins boys,

was determined to find a cave closer to the highway.

He set off alone on a cold winter morning in January 1925

and squeezed into a narrow, twisting crack in the earth,

never before explored.