Covering a diving championship in Greece on a hot and sticky assignment for Outside magazine, James Nestor discovered free diving. He had stumbled on one of the most extreme sports in existence: a quest to extend the frontiers of human experience, in which divers descend without breathing equipment, for hundreds of feet below the water, for minutes after they should have died from lack of oxygen. Sometimes they emerge unconscious, or bleeding from the nose and ears, and sometimes they don't c...