Arecibo Observatory
This 600-ton platform, largest of its kind in the world, is a 20-acre-wide dish set into a gigantic natural depression . Using this telescope, Cornell University scientists monitor pulsars and quasars and probe the ionosphere, moon, and planets. Unlike other radio telescopes, which have a steerable dish or reflector, the dish at Arecibo is immobile; the receiving and transmitting equipment, which hangs 50 stories in the air, may be steered and pointed by remote control equipment on the ground. It has been responsible for several major discoveries, including detection of signals from the first pulsar and proving the existence of the quasar. Tours are available. The observatory is south of Arecibo on Route 111.

Bacardi Rum Factory
On the outskirts of Catano, a ferry ride across the river from Old San Juan, this distillery offers free daily tours of its facilities and drinks on the house served under a huge yellow, bat-shaped canopy. Orange and yellow train-buses carry visitors around the grounds. Each section of the distillery has its own guide. Guests can visit the distillery, the museum, and other sites.

Cabezas de San Juan Nature Reserve
Purchased in 1975 by the Conservation Trust, this 316-acre area is on the island's northeastern tip. It comprises a number of different ecological communities including mangroves, coral reefs, a dry forest, and a series of lagoons. This wide variety of ecosystems in such a small area is part of what makes the reserve so special. It is the only place on the island where all but one of Puerto Rico's natural communities may be viewed in one area - the only missing ecosystem is the rainforest. Tours are available; reservations are required. The nature reserve is off Route 987.

Caguana Indian Ceremonial Park and Museum
Perhaps the most important archaeological site in the Caribbean, this park is run by the Institute of Puerto Rican Culture. Its 10 bateyes, ball courts used by the Indians to play a soccer-like game, are situated on a small spur of land surrounded by fairly deep ravines on three sides. Huge granite slabs along the west wall weigh up to a ton, and a few are carved with faces (half human, half monkey) typical of Taino-Chico culture. The most famous of all the petroglyphs is La Mujer de Caguana, a woman with frog legs and elaborate headdress. The bateyes are bordered by cobbled walkways. The park is on Route 11, west of Utuado.

Culebra
Located 22 miles east of Fajardo, this miniature archipelago consists of the seven-by-four-mile island of Culebra and 23 other islands, cays, and rocks. It still remains relatively unspoiled and set apart from the world. Much of its land, which includes dry scrub, mangrove swamps, and magnificent beaches, has been designated a National Wildlife Refuge. Today, Culebra largely remains a neglected and forgotten backwater, which is what gives it its appeal. It may be reached by ferry from Fajardo or by air from Fajardo or San Juan.

El Yunque (Caribbean National Forest)
El Yunque is well worth a visit for anyone who has ever dreamed of visiting a rainforest. There is a visitor's center, roadside waterfalls, hiking trails, and other facilities. Once a million strong, the colorful Puerto Rican parrot now hovers near extinction and survives only here in the park's outback areas. Tour buses to the rainforest are available. El Yunque is off Route 3, and is about an hour's drive east of San Juan, near the popular beach at Luquillo. If you stop at the beach, you can make this an all-day excursion.

Guanica Forest Reserve
This fine forest reserve protects one of the few remaining expanses of tropical dry forest in the Americas . Attractions include great hiking trails and terrific views. It is around an hour west of Ponce on Route 2. A visit here may be short or long, depending upon whether one goes hiking or not.

Hacienda Buena Vista
Restored by the Conservation Trust, this former coffee plantation (founded in 1833) contains slave quarters, a two-story estate house, and exceptional hydraulic machinery. Tours are available. Reservations are required. The hacienda is about a half-hour drive north of Ponce.

La Parguera
This area contains what is probably the most famous marine attraction in Puerto Rico. The Bahia Fosforescente (Phosphorescent Bay) contains millions of luminescent dinoflagellates, a microscopic plankton. Any disruption or disturbance causes them to light up the surrounding water. Pick a moonless night and take one of the twice-nightly boats (times vary) departing from Villa Parguera's pier. La Parguera is off Route 116 on the southern coast, just west of Guanica, on the way to San German.

Loiza Aldea
This is the sole remaining center of Afro-Hispanic culture on the island. The town of Loiza Aldea was founded in 1719, and its Iglesia del Espiritu Santo y San Patricio (begun in 1646) in the Plaza de Recreo, is the island's oldest active parish church. Its three-day festival, held in July and dedicated to Santo Santiago (St. James), is famous all over Puerto Rico for the beauty and uniqueness of its costumes. Souvenirs are sold in the town, and the scenery as you approach from San Juan is splendid. Loiza Aldea is on Route 187 east of San Juan.

Maricao Fish Hatchery
This hatchery and reserve near Mayaguez has some 25,000 fish (such as black bass and tilapia) in tanks and ponds and a lookout tower. Tours are available. The Maricao Fish Hatchery is on Route 143.

Mayaguez
Despite its reputation as a center of industry, this western port, the third largest city on the island, still retains much of the grace and charm suggested by its lovely name, taken from majagua - the indigenous name for a tree found in the town's vicinity. Mayaguez has a small zoo and agricultural research station. It is on the island's west coast, on Route 2.

Old San Juan
This restored old section of the capital is a remarkable place to visit. It has a number of small museums as well as marvelous restored forts. It is a great place to walk around in and savor the Spanish colonial atmosphere. There is a free motorized trolley that takes visitors around, but it can be faster to walk on your own. Be sure to spend at least a full day here. The old town is at the western edge of San Juan, about a 20-minute taxi or bus ride from the Condado beach area.

Ponce
The island's second largest city, Ponce, has a delightful restored old town with a number of small museums, including an outstanding fine arts museum. The town also has noteworthy outlying sites such as the Tibes Indian Ceremonial Center, which has Taino ruins and a reconstructed village, and the Hacienda Buena Vista, a restored coffee plantation. Great views may be had from Vigia Hill, an outlook in the town's north that has a soaring concrete cross and an old mansion that now serves as the Seralles Museum. Ponce is south of San Juan.

Rincon
The island's chief surfing town lies on the west coast, north of Mayaguez. There is not much reason to visit unl ess you are a surfer.

River Camuy Cave Park
This park taps the island's extensive network of underground caves, which are the result of carbonic acid dissolving limestone over the course of thousands of years. Tours (either 45 minutes or one-and-a-half hours in length) are available for two areas. If you have not spent much time in caves, it is definitely worth the visit. The caves are on Route 129, south of Arecibo and southwest of San Juan. Tour buses are available from San Juan.

San German
The second-oldest and perhaps most attractive town on the island, San German retains its quiet colonial charm and distinguished architecture. Noteworthy sights include an old church, Porta Coeli, which is a museum in itself. Another place worth visiting is Museo de Arte y Casa de Estudio, a small museum on Calle Esperanza 7. San German is on Route 2, near Mayaguez.

Vieques
Set seven miles off the eastern coast of Puerto Rico, this special island possesses its own distinct magic. Horses roam freely all over the island, which is dotted with the ruins of pineapple and sugar plantations and more than 50 magnificent beaches. The downside is that the island contains a military base and is sometimes bombed in certain areas. (The bombing is usually unpredictable. Puerto Rico's government has protested against the use of live ammunition in the wake of several accidental deaths. Getting hit with a shell need not be a concern for tourists.) Vieques may be reached by ferry from Fajardo or by air from Fajardo and from San Juan.