This spectacular and massive cave is named for the aboriginal Guanahatabey. Dripping with limestone formations, it's spooky enough to thrill even grown-ups. Visitors enter the cave through a narrow opening and follow a well-beaten, dimly lighted stone trail for 255 meters (842 feet), narrowing and widening until you reach a high-ceilinged grotto and an underground river. You board a boat here for a short cruise (300 meters [990 feet]) past illuminated stalagmites. The guide points a laser at shapes and if you really use your imagination you can just make out a champagne bottle, a skull, a crocodile, a sea horse, and even the Niña, Pinta, and Santa María. The boat takes you out of the cave through a narrow, vine-draped opening in the rock. Souvenir vendors await as you disembark. Don't miss the chance to have your photo taken atop Tomás, a huge, but placid, water buffalo. His handler will even lend you his straw hat so you can really look the part of a guajiro; a tip is expected. This is a popular spot on the tour-bus circuit, so try to come early or late in the day for a chance to have the cave more to yourself.