This is about one of the most dangerous sports on the planet: cave diving. Just as some of us are driven to climb the highest mountains, these guys (mostly guys) are all about penetrating the deepest and furthest underground in flooded caves and streams. Here your first mistake may be your last and you are well beyond saving if something goes wrong. Quite a lot of it is about how some of them died and their bodies recovered. Much of it goes back to the pioneering days in the sport, where they had no rules and invented their gear as they went- hundreds of feet underground with no wet suits, bcd's or decent regulators, using inflated plastic bottles or whatever they could put together to get themselves deeper. Often they dived alone, and even when they had a buddy they couldn't see each other because of the extremely poor visibility. Taking off your tanks and pushing them ahead of you so you can fit, even having to turn your head sideways without losing your regulator while going through some of the smallest squeezes in complete darkness doesn't constitute my particular idea of fun, but I respect their perseverance. An interesting read for anyone who is into scuba diving, or caving.