Bushman's Hole, on the edge of the Kalahari Desert in South Africa, is one of the strangest places on Earth. It's a prehistoric crater on an otherwise endless track of desert, and for an elite but extreme fraternity of explorers, what happened there is the stuff of myth and legend.
The terrible beauty of the place can't be seen from the air, or even the ground. But if you trace the walls down, you reach a tiny pool covered in algae. Keep going, through a narrow shaft running for another 150 feet, and finally it all opens into a vast freshwater cavern tall enough to hold the Eiffel Tower, and deep enough -- nearly 1,000 feet -- to mesmerize the most experienced, technical cave divers in the world.
Don Shirley is one of only a handful of divers who has "gone deep" at Bushman's Hole.
"It's hypnotic," said Shirley. "When you get permission to dive in a cave, as it were, the cave, it greets you, and you just want to go and explore."
Verna Van Schaik holds the women's dive record there, and said that a good dive propels you to go even deeper.
"That's the lure, that's the danger," she said. "You kind of are able to logic yourself into the fact that the risks probably aren't so real."
The environment in Bushman's Hole is so alien that deep divers compare it to space walking:
"Imagine floating," said Shirley. "So you've got no pull by gravity whatsoever… you're moving around in this cave and you can float up to a ceiling you can float around corners. And if you couple that with silence, then there's absolutely zero noise. That's a magic experience … It is a different world."
Bushman's Hole is the kind of world a young man with a thirst for thrills might love. Theo Dreyer still remembers the day, 10 years ago, when his son Deon was invited by the South African Cave Diving Association to join them as a support diver at Bushman's Hole. Deon Dryer only had two years of diving experience, but it promised to be the thrill of a lifetime.
"They wanted to go deep," said Theo Dreyer. "So [Deon] got invited along to do backup for the guys… He said 'Dad, this is an honor being asked to do this.'"
Exactly what happened on that dive, 10 years ago, is unknown. The dive team reported that while coming back up they looked down and saw Deon Dryer's cave light fading, sinking back into the abyss.
Theo Dreyer said the rest of the group tried a rescue, "but it was futile, he'd gone down too far."
There's a local legend that a man-eating serpent lives at the bottom of Bushman's Hole, but what likely killed Deon Dreyer was something more prosaic, and poisonous.
When a cave diver breathes too heavily at extreme depths -- as an inexperienced diver like Deon Dryer might -- carbon dioxide can build up in the lungs, resulting in a blackout. Deon Dryer never came back from Bushman's Hole.
"The average person, when they pass along, gets buried in a tomb and there's somewhere you can go where there's a living memory and you can go share some thoughts," said Theo Dryer. "We didn't have that. I mean, there was no body. There was nothing."
The memory of Deon Dreyer faded, but Bushman's Hole remained a bright jewel, luring some of the best cave divers in the world. Among them was Dave Shaw. Ten years after Deon Dryer's death, in October 2004, Shaw undertook a kind of dive never attempted at Bushman's Hole.