When seasoned ocean diver Michael Agar tries his hand at cave diving, he finds--once he overcomes those fear "gremlins"-- that there's a whole other world down there. Traveling to the state of Quintana Roo, Mexico, which stretches along the tropical Yucatán coast south of Cancún, Agar is guided in his dives by Kay and Gary Walten, who explore and map new cave systems when they're not guiding the growing numbers of sport divers who come to follow the caves' marked trails of nylon line. Even by the standards of extreme sports, Agar discovers, things are moving very fast in Yucatán cave diving; after all, it was only a little over a decade ago that serious exploration of the caves began.
"We leave the warm green glow of the entrance behind," writes Agar; he then enters a dark world of linked underwater spaces so elaborately decorated that they bear names like "Ice Age" and "Candy Store." Between dives, he learns how the caves came to be formed; why they have been so important to the Maya through the centuries; what kinds of growing pains have accompanied the rapid development of cave diving as a sport in Quintana Roo; and how the cave explorers themselves go about mapping the meandering passages of the Yucatán's flooded basement.