There is a limestone cave in Western Virginia where one of its giant chambers has been turned into a musical instrument.

They call it an organ, but it's like no other organ on the planet.

It relies on electromechanical mallets, steel bolts, electric guitar pickups, and the main vibrating material, limestone.

It's more technically referred to as a lithophone, the only one of its kind in the world, but people around here just call it the organ.

So Veritasium producer Petr went to check it out.

We're going underground. Let's go. Can you tell me a little bit about the history of this place?

Luray Caverns?

Yeah.

Discovered 1878, and, in fact, to your right is where they first came in.

Oh, no way.

On August 13th, 1878, a group of hunters felt a cool breeze coming from a small hole in the ground.

Putting down their rifles, they began to dig, making a hole big enough for the smallest of them to fit through.

Andrew and Quint had only a candle for light as they lowered themselves down into the hole.

They spent the next few months exploring.

They kept finding giant caverns connected by narrow passageways.

The ceilings and floors were covered in stalactites and stalagmites.

They even found an underground lake.

The cave system they had accidentally stumbled upon turned out to be the largest in the Eastern United States, covering 26 hectares.

It's now known as the Luray Caverns, and it's visited by half a million tourists each year.

That's Dream Lake.

How still that water is and the reflection is just really something else.

The organ is one of the lower areas. It's in a room called the Cathedral, a very large room.

Yeah, that makes sense.

And they used to have dances down there, balls. They used to call it the ballroom before the organ was put in.

Oh, no way. So in the 1920s, people would go down here and have

Oh yeah.

balls and dances and

Well, it was no-

shindigs.

It was a great place because it's air conditioned basically naturally, so.

Yeah, that makes sense. Oh my God. Are you kidding me? No way. Oh, this is so gorgeous.

(riveting instrumental music)

And there's the control panel for the organ.

That's the organ. You're actually inside the organ right now.

The organ covers three and a half acres.

All the notes are scattered out around us.

Of course, this was started in 1954, first played in 1957.

Okay. So it took three years to get from-

Yes.

Welcome to the beautiful caverns of Luray in Luray, Virginia and particularly to the Great Stalacpipe Organ, which is located in this great cathedral-like structure, which is 260 feet below the surface.

This organ is so huge that you stand not before it but within it.

In 1954 while on a tour of the caverns for his son's birthday, Leland Sprinkle, a mathematician who worked at the Pentagon, had an idea.

See, during the tour, the guide walked around with a small mallet.

He would occasionally hit a stalactite, producing a musical tone.

This was the start of Sprinkle's three-year project to turn the cave into a musical instrument.

Since you asked for it, we shall be most happy to show you how we make music from the ancient stalactites around us.

What he did is he walked around these caverns with a ladder and climbing equipment and little mallets and little tuning forks, and he would hit on stalactites.

And then when there was one that was close enough to concert pitch that he wanted, he'd take a disc grinder and grind off the stalactite until it came to the pitch that he wanted.

So this one should be middle C.

(soft jaunty music)

(sound chimes)

Stalactites form very slowly.

In this cave, they grow at around 16 cubic centimeters every 120 years.

The rate is dependent on the amount of water that flows.

So some stalactites grow quickly while others don't really grow at all.

They form as slightly acidic water flows through the ground.

It dissolves the limestone and then redeposits it when it comes in contact with the air.

As the water drips to the ground, it can also deposit the limestone on the floor, leading to a stalagmite.

Sometimes over thousands of years, the stalactite and stalagmite can fuse together, forming a column.

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(soft chiming music)

If you tap on a stalactite, then like a tuning fork, it vibrates at its resonant frequency.

That frequency depends on the size and shape of the stalactite.

Bigger stalactites make lower notes, and it also depends on the elastic modulus of the material.

In this case, it's all limestone.

So to adjust the resonant frequencies, Sprinkle shaved a bit off the end of some stalactites, putting them into concert pitch.

The organ wasn't connected to the console when we visited, so Petr didn't get a chance to play it.

But Rob Scallon, who has a great YouTube channel, made a video about it a couple years ago.

We asked him what it's like to play a cave.

It's hard to describe the feeling of playing a cave.

(keys echo)

It's very like grounding, very surreal, very beautiful.

You know, if I'm being romantic about it, you can hear the eons and eons and eons of time that were needed to create this thing.

The cave is, of course, huge, and all the notes are in different places.

So some are further away. Some are closer.

Some are amplified near you, some aren't, and I love reverb, and the amount of reverb in this room is just so immense, and the notes are so pure and beautiful, and they're in different places.

So they like have different reverb.

It's a very like hauntingly beautiful type of sound.

As you can see, there's also the solenoid that is basically a mallet.

After the tuning has been completed, we design a custom built bracket to which we attach an electrically operated plunger.

This plunger with its rubber tip strikes the stalactite, causing it to vibrate.

Since different musical stalactites are far away from each other and their volume variable, Sprinkle amplified the vibrations.

He could've used microphones, but in the 1950s, those weren't particularly robust.

So instead, he borrowed an idea from a piece of technology invented in the 1930s, the electric guitar pickup.

(upbeat electric guitar music)

A guitar pickup is a coil of wire wrapped around a magnet.

When a steel guitar string vibrates near it, it interacts with the magnetic field, which induces a current in the wire.

It doesn't work with non-metal guitar strings.

The thing that's vibrating needs to be ferromagnetic.

Sprinkle added a steel bolt to each of his musical stalactites and then used a pickup to detect the vibrations.

These signals are amplified mixed and played back through speakers.

You also gotta consider the weight of the bolt that goes into.

Oh, right.

Yeah.

But the guitar pickups created an unexpected problem, radio interference.

I don't know exactly how it works, but one of the keys was picking up a local radio station, which actually turned it into a sampler.

It was a really fun part of the video and actually sounded pretty cool.

That happens with electronic instruments sometimes, even caves. (laughs)

(keys echo)

(muffled singing echoes)

What is that? It happens every time I hit that key.

(keys echo)

(muffled singing echoes)

I'm like turning on the radio.

It is picking up on that signal.

(people laugh)

Oh my God.

That is what it is. You're getting keys.

So the radio is here.

(voices echoes)

I thought, I'm like, "Is that a human voice?" Like is that-

That would be the AM radio. AM station across the street.

If they were tuned in, you know, 1957, have they become longer and hence gone out of tune?

Well, he tried to pick stalactites that are inactive, that aren't growing anymore is what he tried to do.

But if he found stalactites that were growing 'cause I'm seeing like a little bit of water, right?

Yeah, and you'll see-

There's a little bit of growth happening.

Right, and you'll see that, and that comes and goes, but we've never had to retune one yet.

Like I love the idea that there's an organ that could grow out of tune

It could.

because of how stalactites grow.

I don't think it'll be in my lifetime, but it could.

(Larry chuckles)

If he chose a bunch that weren't inactive, it would be out of tune already.

Oh yeah. If they were completely active, it would be.

That's so cool.

It's very mad scientist.

He definitely couldn't get away with it now, like going into a place like this and then just starting to shave off the stalactites that took eons to be created by nature.

Thankfully it stays in tune 'cause I can't continue shaving off the parts of this cave.

This is just such a strange and beautiful and kind of insane project to take this gorgeous cavern and make it even more beautiful by turning into a musical instrument.

This structure has been being created drop by drop for an unfathomable amount of years, and that's pretty awe inspiring.

(electronic beeps trill)

(organ keys echo)