(Really) Risky Business

Most of those who have died lacked formal cave-diving training. But sometimes, even veteran cave divers get too cocky for their own good. And even if experienced divers take all of the right precautions, they're still not guaranteed a safe return. One of the best, a friend of Skiles's named Parker Turner, died at a place near Tallahassee called Indian Springs. Part of the cave collapsed, plugging the way out. Turner clawed through the debris, almost reaching the cave's upper chamber, before running out of air. His partner followed the path that Turner had cleared -- and survived.

After Turner's death, Skiles stopped recovering bodies. The emotional toll was just too great. But Skiles still dives. The question is, Why? What makes it worth the risk?

Skiles doesn't hesitate before answering: Underwater caves are one of the last frontiers on Earth. They are places of beauty and wonder that only a handful of people have explored. Where others see a black hole, Skiles sees what he calls the "nothingness highway" laid out before him, and he wants to be the first to cruise down that road -- the first to shine a light on these underwater labyrinths and discover a new maze of tunnels, or a grave of mastodon bones. For him, journeying into a virgin cave system is like discovering the Grand Canyon -- while flying.

Of the many dives during which Skiles pushed himself to the edge of human experience, one moment stands out. He was with a team that was attempting one of the first mixed-gas cave dives -- using mixtures of helium and oxygen to enable them to drop more than 300 feet deep into Florida's Wakulla Springs. (At that depth, a diver will deplete a normal tank of air in 30 breaths.) Skiles and his team had pushed more than 2000 feet into a large, dendritic tunnel that broke off into smaller and smaller passageways, like the branches of a tree. They hit a depth of 320 feet and then started up a steep slope. When they broke over the top of the hill, the divers found themselves in an enormous chamber that soared to a height of 250 feet. In the center was a 7-foot spire of boulders, capped by a pure-white rectangular stone standing on its edge.

Skiles and the other divers stared in absolute awe. "That great slab of rock was a mirror image of the monolith in the movie 2001: A Space Odyssey," recalls Skiles. "It struck me at that moment that just like in the movie, we were using advanced technology to visit and explore an alien world. But in another sense, we were really the most primitive of beings. We all got chills. We named that place the Monolith Room."

His Options Are Always Underwater

It's nearly a theological concept in cave diving: Take two of everything. Your equipment is your life support, and every diver who ventures into an underwater cave brings backup gear -- tanks, regulators, lights, computers. That way, when a light goes out or a hose pops, the diver still has a very good shot at getting out alive by relying on the backup equipment.

But the one piece of equipment that cannot fail is your brain. "Your mind is your regulator," says Skiles. "It takes a constant inventory of your body, your gear, and your environment. If all systems are go, your mind controls your pace, your rate of breathing, and the ways that you reevaluate the risks as you go deeper into a system. Cave diving is the ultimate cognitive undertaking. People compare it with an endurance race, but it's really more of an extreme game of chess."

The risks increase exponentially as divers push ever farther into a system. On deep dives -- and a place like Wakulla Springs is a very deep dive -- nitrogen builds up in the body. Unless divers spend time in shallower water letting gas bleed out of their system, they will suffer decompression sickness, more commonly known as "the bends." So divers must constantly manage their depth. And that can mean keeping track of as many as eight regulators and eight pressure gauges of the gas mixtures that they are dealing with, as well as the guideline -- that umbilical cord back to the land of the living.

That's not all. As they push farther into the deep, divers endure a form of psychological stress called "perceptual narrowing." Sensory overload begins to take its toll, and they become less and less aware of their surroundings.

"You start to get that 'way-back-in-the-earth' feeling," says Skiles. "You know that you've passed the edge of normal human experience, but you don't know how far you've gone. In mountain climbing, you can see the summit, the lofty goal. In underwater-cave exploration, no one knows what's down there. You can't quantify whether you're halfway there or three-quarters of the way there. The weight of the unknown really bears down on you. When you get back into these deep places, you're so perceptually narrowed that you can't understand the nuances of what you're seeing and what you need to do in order to survive."