Parque de Las Cavernas del Río Camuy, Camuy
Tel: 787 898 3100
Concierge.com's insider take:
This stunning series of underground caverns, about 70 miles southwest of San Juan, encloses one of the largest subterranean rivers in the world. A tram takes you down a corkscrew trail to Cueva Clara, where stalactites and stalagmites resemble the fangs of some fearsome creature. Besides underground rivers and weird rock formations (including one a guide swears resembles Julia Roberts), there are otherworldly creatures like blue-eyed river crabs and furry-legged tarantulas. There are also more than 100,000 bats, but it's rare to see them during the day.
Open Wednesdays through Sundays 8 am to 4 pm.