[MUSIC PLAYING] (narrator) It looks like the wall from Game of Thrones or Superman's fortress of solitude.

Except this frozen marvel was made by human hands-- a mile long and 150 feet tall.

The substance it's made of, you might think you know, but it's far stranger than you ever imagined.

[MUSIC PLAYING] In the rugged mountains of Southwest Colorado lies the town of Ouray, known as the Switzerland of America.

Every year, the canyon on the edge of town is transformed into a fantasy land of ice.

The Ouray Ice Park is the world's largest man-made ice park for climbers.

(Kim Reynolds) This park is like nothing else.

There's no there's nowhere in the world like it.

(narrator) It attracts visitors from around the world.

(speaker) I was intrigued from the first time that I visited a park-- "Woah, I wonder what goes into that.

How do they create all this ice?"

(narrator) Xander Bianchi is one of just a handful of people on the planet who knows the secrets to making these frozen falls.

He and his park co-workers call themselves ice farmers.

(Bianchi) It's been an oral tradition for many years.

There is no handbook.

There's no manual, no textbook on how to do this.

(narrator) The icy delights they raise may be seasonal, but they don't get taken to market and they grow from the top on down.

This park started out modestly.

Twenty-five years ago, it was just a couple climbers and some garden hose.

Today, the 300 sprinklers and spouts spew 300 gallons a minute.

(Bianchi) And that's all water that would normally just be dumped into the river.

It's excess water from the city of Ouray.

(narrator) Instead that water is routed through a complicated network of pipes and valves.

(Bianchi) And it's above-ground plumbing in the wintertime, non-insulated pipes.

It works but it barely works.

The sprayers kind of act is like a fertilizer.

When it's cold out and we're running sprayers, it just kind of explodes.

It grows a lot of ice.

If it's colder out, a lot of that water will freeze before it even hits the cliff.

(narrator) That can lead to strange ice formations called Dragon's Breath.

(Bianchi) If you've ever seen a dragon breathing ice, that's what it looks like.

(narrator) How do you avoid ice monsters and make formations that are actually good for climbing?

(Bianchi) So there's a few tricks that we use to create different formations.

Water is a polar molecule, which means that it has a slight charge to it.

So it likes to stick to things.

So we use either ropes or chain, and we'll attach that to the cliff.

And when we run water above that, the ice forms on that.

It's like a starter for a freestanding pillar.

(narrator) When a pillar reaches the ground, it usually becomes strong enough to climb.

When it doesn't touch down, it can become dangerous "hangfire."

(Bianchi) Hangfire is just a term we use to describe daggers that could come loose and hurt somebody.

(narrator) So how do you get rid of a couple-hundred-pound popsicle of death?

(Bianchi) Whoo-hoo!

(Bianchi, narrating) We're going down on a rope and we're swinging at a giant icicle with an ax.

(narrator) They call it "trimming the crops."

(Bianchi) Yeah!

(narrator) Another challenge of ice farming is something they call "eggshell."

After a new snowfall, a layer of ice can often form on top of it.

(speaker) What's underneath is this very fluffy, very light dry snow as if it had just fallen.

(narrator) That leads to weak and unstable ice.

(Carrion) Before eggshell forms, we have to get down there and basically smash this layer of eggshell ice and send it into the gorge.

(narrator) As incredible as this place is, the substance it's made of might be even more wondrous.

Brian Woodfield studies low-temperature phenomena and has seen up close the oddities of water.

(Woodfield) What you can do is a phenomenon called super cooling.

You cool pure water, and you cool it slow enough that you can cool it below 0 degrees C. And then you can cause it to instantly change into the solid.

(narrator) Yes, that's right.

Water doesn't always turn to ice at 0 degrees Celsius.

Ice needs a seed to form around-- dust, pollen, or in this case, other ice crystals.

(Woodfield) It wants to transform, but if you got really clean water with really clean surfaces, then it doesn't know how to do it.

You drop in this little piece of ice.

Immediately water molecules in the vicinity of that ice as it enters starts bonding.

And it just goes as fast as possible.

When you make these crystals, these atoms and molecules are going into their locations.

How fast you do it, though, governs how well-organized it goes in.

So the faster you freeze it, the more floors that crystal is going to have.

When you see these whiskey commercials, you'll see this most beautiful ice ever made, no imperfections.

And that ice was grown really slowly to make it look perfect.

When you get to a really well-made ice crystal, you're going to see that it's much stronger.

It's going to be harder to go break that.

(narrator) Ice that's perfect for the glass has some similarities with ice that's perfect for climbing.

Freezing gradually over time is the key to creating ice that can support climbers.

(Woodfield) It's a natural slow process.

There's no fast way of doing it.

That's super hard that's a massive undertaking.

(narrator) After several weeks of slowly coaxing ice to bloom on these cliffs, it's time to open the park.

But to create the most ideal ice for climbing, the farmers have to again count on Mother Nature.

They need temps that aren't too cold or too warm.

The best is right around freezing, which makes the ice less brittle and more malleable.

It becomes what they call "plastic ice."

(Bianchi) It takes on this quality of being plastic.

It absorbs the blows from picks really well.

Some people also refer to it as "hero ice" because you feel like a hero when you're climbing it.

It's just so easy.

(Carrion) You have somebody from across the world climb it and tell you how amazing it was.

I mean, it feels good, and we do take a lot of pride in making the best that we can.

[MUSIC PLAYING] Hey, guys, thanks for "chilling out" with us and watching that "super cool" episode-- Okay, I'm sorry, that was bad.

Buy, hey, thanks for watching Overview, and make sure you're subscribed here on PBS Terra so that you don't miss the next one.

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