Cave diving is among the most challenging and treacherous sports in the world. In the underground rivers of the Yucatan in Mexico miles of uncharted tunnels and awe-inspiring caverns have lured the world's greatest divers to brave the perils of its labyrinthine passageways. From a cave entrance deep in the jungle, diver Mike Madden has charted over 50 miles of breathtaking dives to azure blue underwater worlds.