An adventurous look into sunken caves and other sinkholes, including the famous sacrificial well of the Mayans in Yucatan, the underground springs and caverns of Florida (where mastodon bones were discovered in 1955 along with a child's skeleton carbon-dated to 5000 B.C.), and similar subaqueous chasms where the threat of death is seldom distant. Also described are some dives by Jacques Cousteau's team in the Fountain of Vaucluse near Avignon, where a normally placid pool boils fantastically every spring. The panic and beauty of the first sightings of grandiose limestone caverns, enormous stalactites and weird Coleridgean settings are affecting and neurasthenic readers won't forget the Stygian blackness in thirty feet of mud in the Mayan well where a flashlight can't be seen. No matter how scientific the planning, you bet your life on each journey down in a hot/cold sweat.