Rivers Into the Unknown (2000)

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.