El Yunque (tel. 787/888-1880 for information): Forty-five minutes by road east of San Juan in the Luquillo Mountains and protected by the U.S. Forest Service, El Yunque is Puerto Rico's greatest natural attraction. Some 100 billion gallons of rain fall annually on this home to four forest types containing 240 species of tropical trees. Families can walk one of the dozens of trails that wind past waterfalls, dwarf vegetation, and miniature flowers, while the island's colorful parrots fly overhead. You can hear the sound of Puerto Rico's mascot, the coquí, a small frog.

Río Camuy Caves (tel. 787/898-3100): Some 2 1/2 hours west of San Juan, visitors board a tram to descend into this forest-filled sinkhole at the mouth of the Clara Cave. They walk the footpaths of a 170-foot-high (51m) cave to a deeper sinkhole. Once they're inside, a 45-minute tour helps everyone, including kids, learn to differentiate stalactites from stalagmites. At the Pueblos sinkhole, a platform overlooks the Camuy River, passing through a network of cave tunnels.

Las Cabezas de San Juan Nature Reserve (tel. 787/722-5882): This 316-acre (126-hectare) nature reserve about 45 minutes from San Juan encompasses seven different ecological systems, including forestland, mangroves, lagoons, beaches, cliffs, and offshore coral reefs. Five days a week (Wed-Sun), the park staff conducts tours in Spanish and English, the latter at 2pm only. Each tour lasts 2 1/2 hours and is conducted with electric trolleys that traverse most of the park. Tours end with a climb to the top of the still-working, 19th-century lighthouse for views over Puerto Rico's eastern coast and nearby Caribbean islands. Call to reserve space before going, as bookings are based on stringent restrictions as to the number of persons who can tour the park without damage to its landscape or ecology. The cost is a relative bargain, $5 for adults, $2 for children under 13, and $2.50 for seniors.