The beguiling network of stalagmite-ornamented caves at Río Camuy is the third-largest network of its kind in the world, formed by the soft karstic limestone that shapes the hills on this remarkable part of the island. This park is big – it's spread over 10 miles and has multiple entrances. A visit here can be an unearthly, slightly creepy diversion from the typically sunny shore, if you have the time and patience to put up with the terrible crowds.
Over the years, the caves have been shelters for indigenous people, home to millions of bats that help keep the island’s insect population under control, and a source of fertilizer. But no modern explorers went to the trouble of making a thorough investigation of the caves until 1958. In 1986 the attraction opened as a tourist facility.
Call the park for local conditions (too much rain causes closures) and arrive before 10:30am to avoid the worst crowds or waits of upward of an hour standing in line. Don’t expect much contact with the spectacular underground formations either. Your visit begins with a film at the visitors center and a trolleybus through the jungle into a 200ft-deep sinkhole to Cueva Clara de Empalme (Clear Cave Junction), where you take a 45-minute guided walk. Here you walk past enormous stalagmites and stalactites. At one point the ceiling of the cavern reaches a height of 170ft; at another you can see the Río Camuy rushing through a tunnel.
After leaving the cave from a side passage, you take another tram to the Tres Pueblos sinkhole, which measures 650ft across and drops 400ft. Forty-two petroglyphs that you can now inspect have been found in Cueva Catedral (Cathedral Cave).
The last tour leaves at 2pm if you want to see all three areas. All told, the fun of the visit here depends on the size of the crowds, your patience and the tour guide (some of them seem bored stiff).