Not to miss

San Juan

San Juan is a spirited modern city with high-rise beach strips and a justly famous colonial core. Founded in the 16th century, it's the second-oldest city in the Americas; today it's the engine of the island's economic and political life and the cultural beachhead for US influence in the Caribbean.

Many Caribbean adventurers never make it past Puerto Rico's seductive capital: there's a lot to be said for being able to lay a towel down on a pristine white Caribbean beach while having the culture and quaintness of a historic city and the convenience of a modern metropolis just minutes away.

Ponce

Nearly half a billion dollars have been spent preserving the colonial core of Puerto Rico's second city, and it's not only architecture buffs who declare the money well spent. The heart of Ponce dates from the late 17th century and has been declared a national treasure.

It consists of plazas and churches and highly decorative colonial homes, some glorious fountains and what may well be the funkiest fire station in the world. One of the reasons Ponce is so easy on the eye is that an early city regulation required that street corners be chamfered (curved).

The architectural curvaciousness was designed to make it easier for carriages to pass and to carry wooden houses from one site to another. Ponce is a fraction inland on the central southern coast, and the locals are a breed apart from their brash northern cousins. They are justifiably proud of their civic heritage, the centrepiece of which is the stately Cathedral of our Lady of Guadeloupe. The city's reputation as a centre of cultural excellence comes in the modern form of the Ponce Museum of Art, the best in the Caribbean. If you're a sucker for a vista, the plexiglass Cruceta el Vigia just north of the centre looks over Ponce to the sea.

Río Camuy Cave Park

This jagged karst region in the northeast of Puerto Rico is littered with sinkholes and surreal limestone formations, making it prime spelunking territory. Over 200 caves have been discovered in the region, some capable of swallowing skyscrapers.

The Camuy River is one of the largest subterranean rivers in the world. Experienced cavers can get dirty and wet by climbing, scrambling, abseiling and swimming through the underground river system, but some experience is required to contemplate entering this dangerous terrain.

Mere mortals can get an antiseptic version of these thrills by riding a trolley-tram into a sinkhole and accessing Cueva Clara, which is graced with both stalagtites 'n' mites. From the safety of viewing platforms, you can glimpse the Camuy River as it flows past the 120m (400ft) deep Tres Pueblos Sinkhole.

Iglesia de San José

The Iglesia de San José is the second-oldest church in the Americas. Established in 1523 by Dominicans, this church with its vaulted Gothic ceilings still bears the coat of arms of conquistador Juan Ponce de León (his family worshipped here), a striking carving of the Crucifixion and ornate processional floats.

For 350 years, the remains of Ponce de León, Puerto Rico's first governor, rested in a crypt here before being moved to the San Juan Cathedral down the hill. Several historical figures are buried here, including painter José Campeche, who painted several churches on the island.

El Yunque

Tourist authorities are fond of promoting this reserve as the only tropical forest in the US national park system. The Taínos believed the god of happiness hung out on El Yunque, and you'll understand why when you hike through this magnificent rainforest. On a clear day you can even bag an eyeful of the Virgin Islands.

Covering 11,200 ha (28,000 acres) in the Luquillo mountains, this bountiful lush rainforest is home to more than 400 tree and fern species, most of which thrive in the hothouse conditions. There are 13 well-maintained hiking trails in the reserve, ranging from leisurely 15-minute wanders along sealed paths to a heart-pounding trek to the peak of El Yunque. If you stretch your legs in the rainforest, you'll hear the sing-song of the coquí frog (Puerto Rico's national emblem), see miniature orchids, get to play in waterfalls and maybe even glimpse the rare Puerto Rican parrot. El Yunque is less than an hour drive from San Juan, and there's road access to the reserve.

Plaza Las Delicias

The Plaza Las Delicias or 'Plaza of Delights' is the quintessential Spanish-colonial plaza. In the daytime the square is filled with strolling shoppers, children playing and groups of elderly men enjoying a quiet game of dominoes under shade trees. A string of pretty cafes and eateries circle the park.

The plaza is at its best at night, when violet and pink lights dance in the waters of the Fuente de Leones (Fountain of Lions), a monument rescued from the 1939 World's Fair in New York. In the shadows, statues of island legends like Luis Muñoz Marín and famous danza composer Juan Morel Campos fix their eyes on eternity.

Bosque Estatal de Guánica (Guánica Biosphere Reserve)

Make sure you stop by the ranger station to pick up some maps before exploring this marvellous park. You can take a half-hour hike to a beach through three different kinds of forests, tramping the coast until you find a secluded cove for sunning yourself, before hiking back to your car by a different trail.

And all of this takes place in an area where birds, bullfrogs, the pale blue Caribbean and the sunshine make music together. The forest's uneven rainfall and drainage patterns have created an unusual variety of habitats for more than 700 varieties of plants (48 in danger of extinction), which attract a large number of birds. Some studies claim that at least 40 of the 111 species of birds found in Puerto Rico turn up in Guánica. Everyone agrees that Guánica is a preferred habitat for nine of the island's 14 endemic species, which include the Puerto Rican woodpecker, the Puerto Rican emerald hummingbird, the Puerto Rican lizard cuckoo and the Puerto Rican nightjar, which is one of the island's highly endangered species. With 36 miles (58km) of trails and over 10 miles (16km) of undeveloped Caribbean coastline, Guánica is a first-rate attraction to nature lovers.

Arecibo Observatory

Tucked away in the gorgeous backroads of northwestern Puerto Rico is the largest single-dish radio telescope in the world - an impressive 1000ft (305m) in diameter and covering about 20 acres (8ha). The observatory is recognised as one of the world's most important research facilities.

Scientists and engineers from all over the globe come to measure all sorts of technical science-y stuff while gazing at the night sky. The facility is operated by Cornell University and scientists here reach out to the likes of ET with the ongoing Search for Extraterrestrial Intelligence (SETI) program. There's an excellent interactive science and space museum on site.