This island of tropical breezes is little known to British travellers, but as Stephen Keeling reveals, it offers wild beaches and historic sites within easy reach of a lively capital city

Remind me where it is again...

This mainly Spanish-speaking island poses prettily midway between the Dominican Republic and the Virgin Islands. Puerto Rico is the fourth-largest isle in the Caribbean, and about the same size as Cyprus. The island was colonised by the Spanish early in the 16th century. Despite numerous Dutch, French and British attacks, it remained a Spanish possession until the Americans took control in 1898.

The capital, San Juan, vies with Havana, Santo Domingo and Kingston for the title of "capital of the Caribbean". It is one of the largest and most dynamic cities in the region. Yet beyond the city much of the island remains surprisingly undeveloped: you can dive or snorkel in warm waters swarming with marine life; explore rambling old colonial towns; clamber over castle ruins; visit gourmet coffee plantations; dance the night away at a salsa club; hike through jungle-smothered towers of limestone; or feast on barbecued pork at a roadside stall. And the beauty of Puerto Rico's modest size is that few places are more than an hour's drive from San Juan.

Puerto Rico has been a "commonwealth" of the United States since 1952. This provides huge economic benefits (the island is one of the richest in the Caribbean) and self-government in domestic affairs, while retaining a degree of cool separation from the mainland. The currency is the US dollar, and the US connection means you'll be able to speak English in many parts of the island.

Where to start?

Old San Juan, a beautifully preserved slice of 18th-century Puerto Rico (and just half an hour from the island's international airport). This is where the Spanish established their first permanent settlement on the island in 1521. Exploring its narrow, cobbled back lanes is a magical experience, with salsa music drifting out of half-opened wooden doors and wrought-iron balconies smothered in flowers and fan-shaped palms.

The old town is littered with absorbing museums and churches. Foremost is El Morro (001 787 729 6960; tiny.cc/3cQdc), the imposing stone fortress that guards San Juan Bay. It opens 9am-6pm daily (to 5pm from June to November), admission $3 (£2).

Old San Juan is an excellent place to stay while you explore the city and its hinterland. Da House Hotel at Calle San Francisco 312 (001 787 977 1180; dahousehotelpr.com) is a real bargain, with simply furnished rooms enhanced with Spanish tiled floors and paintings from local artists. Doubles start at $90 (£60) – excluding breakfast, which is always the custom in Puerto Rico except at B&Bs.

For historic character and a lot more luxury stay at the Hotel El Convento at Calle Cristo 100 (001 787 723 9020; elconvento.com), a tastefully restored 17th-century Carmelite convent (double rooms start at $300/£200).

The beaches of nearby Condado and Isla Verde offer a change of pace, as well as a plethora of big, upmarket resort hotels along the ocean front. If you can live without a giant pool, opt for the San Juan Water & Beach Club Hotel at Calle Tartak 2 (001 787 728 3666, waterbeachclubhotel.com). This is the city's top boutique hotel, with a roof-top bar and stylish, all-white rooms (from $180/£120).

I want to burn some calories

On the southeast coast, inside the Palmas del Mar development, Rancho Buena Vista (001 787 479 7479; ranchobuenavistapr.com) provides a wonderful opportunity to ride thoroughbred Paso Fino horses along sandy beaches. The islanders are immensely proud of their unique horses: only the Puerto Rican-bred Paso Fino is born with the four-phase gait prized at international competitions. The standard trail rides ($45/£30) last around one hour.

You can find ideal hiking territory just 26 miles from San Juan at El Yunque National Forest (001 787 888 1880; fs.fed.us/r8/caribbean). The reserve is laced with well-maintained trails, hundreds of tropical birds, scurrying green lizards, and a chorus of coquí frogs – the national symbol. Get maps and information at El Portal Rain Forest Centre (daily 9am-4.30pm; $3/£2) at the entrance.

Some of the most enticing B&Bs can be found on the fringes of El Yunque National Forest, such as the Rainforest Inn on highway PR-186 (001 787 809 8426; rainforestinn.com), which has three villas on a tranquil five-acre estate (from $147/£98, including breakfast).

Where else can I stay?

Accommodation prices come down outside the capital, and for budget travellers there are one or two hostels. One such can be found on the west coast: the Rincon Inn (001 787 823 7070; rinconinn.com), where a bed in a dorm costs $25 (£17) a night. Otherwise, the cheapest places tend to be small, family-run hotels. Expect to spend at least $70 (£47) for a basic double.

Steer me off the beaten track

Hit the mountains. With a car, you can explore the Ruta Panorámica, an interlocking network of several rural highways, following the highest ridges of the Cordillera Central for 165 miles. The route slices through the physical and spiritual heart of Puerto Rico, a world of small coffee plantations, mist-shrouded peaks and isolated forest reserves. Take a short detour to the Centro Ceremonial Indígena de Caguana (open daily 9am-4pm except Monday; $3/£2), a rare remnant of the island's Taíno civilisation.

The Taíno were virtually wiped out after the Spanish conquest, and we know little about the enigmatic ball-courts here, some of which are inscribed with petroglyphs. It seems likely that Caguana operated as a place for ceremonial games.

Further west, Maricao makes an intriguing stop, a languid mountain town lauded for its coffee, strong enough "to keep the devil awake".

To the beach...

On the main island, fashionable Isla Verde is the pick of the San Juan city beaches,u o but for clearer waters and a spectacular mountain backdrop, head east to Luquillo, a day-trip from the capital. With more time, hit the west coast, where rustic Playa Buyé is shaded by portia trees, and the curve of Balneario de Boqueró*is backed by a thick crust of palms.

The offshore islands of Vieques and Culebra boast some of the most idyllic coastlines in the Caribbean. Thanks to their occupation by the US Navy until recently, both places were spared the excesses of tourism. On Vieques, the powdery sands of Media Luna, the sweep of Sun Bay, and the reef-encrusted coves of Green Beach top a line-up of unapologetically wild beaches.

Casa Ladera (001 917 570 7558, casa-ladera.com) is a great deal for families, containing three two-bedroom units with kitchens and access to a large pool. Rates start at $1,300 (£867) for a week. Inland, the Zen-like Hix Island House (001 787 741 2302; hixislandhouse.com) offers 13 modernist studios completely open on one side to the forest (modest guests can roll down a screen). Doubles start at $226 (£151). Playa Flamenco over on Culebra is spellbinding, and is also often devoid of people.

You can fly from San Juan to Vieques with Vieques Air-Link (001 787 741 8331; vieques-island.com/val), and to Culebra with Air Flamenco (001 787 742 1040; airflamenco.net). Flights cost around $60-70 (£40-47) each way.

Blow me away

How about a lagoon that glows in the dark? Thanks to microscopic creatures known as dinoflagellates, Puerto Rico is home to the truly bizarre phenomenon of bioluminescent bays. Boats and kayaks leave ghostly trails in the water, while swimmers are engulfed by luminous clouds, droplets spilling off their hands like sparkling diamonds.

The best example can be found on Vieques, where Island Adventures (001 787 741 0720; biobay.com) offers boat tours of Puerto Mosquito for $32/£21. It's crucial to avoid a full moon, when the sky is too bright.

What should I eat?

Puerto Rican food is a tasty blend of Spanish, Taíno and African cuisine known as cocina criolla. Start with mofongo, the starchy but addictive national dish, where plantains are mashed with garlic and olive oil, then stuffed with meat. It's best experienced at Ajili-Mójili (001 787 725 9195), an elegant restaurant at Avenida Ashford 1052 in San Juan (from $21/£14). But what Puerto Ricans really miss when they live abroad is a bowl of rice and beans (arroz con habichuelas).

The central mountains are all about barbecue, with smoked chicken, home-made sausages and lechón (roast pig) sold from roadside stalls. The highest concentration can be found in Guavate on PR-184, a short ride from highway PR-52, about 45 minutes south of San Juan. At Lechonera El Rancho Original (001 787 747 7296), a big plate of pork and plantains is just $5/£3.

Don't leave Puerto Rico without sampling kiosco cuisine: mouth-watering fritters, pinchos (kebabs) and other slabs of seafood fried up in simple shacks for a handful of change. Common kiosco fare includes bacalaítos (plantain pancakes deep-fried with mashed cod), and alcapurrias (more substantial fritters made from mashed plantain and yautía root, stuffed with ground beef or seafood such as crab). The best kioscos can be found in Piñones, just outside San Juan, and Luquillo, a short drive east along the coast.

And drink?

The island is one of the world's largest producers of rum (or ron, as it is known). The biggest locally produced brands are Bacardi and Don Q, though real connoisseurs should try Ron de Barrilito; this rich, dark spirit was created in 1880 and is aged in Spanish sherry barrels for a minimum of three years.

Puerto Rico's national drink is the piña colada, a combination of rum, pineapple and coconut. Its origins, though, are disputed. The official claimant is bartender Ramon "Monchito" Marrero, who is said to have invented the cocktail while working at the Caribe Hilton in 1954. However, if you visit the Barrachina restaurant at Calle Fortaleza 104 in Old San Juan, a marble plaque on the street claims that Don Ramon Portas Mingot created the drink there in 1963.

The truth is that no one really knows who invented piña coladas – they were being made in Cuba at the turn of the century, where they literally were just non-alcoholic "strained pineapple" drinks. However, some aficionados claim the alcoholic version was mentioned in travel magazines as early as 1922 with reference to Cuba – the home of the mojito.

How do I get there?

Direct flights no longer operate between the UK and Puerto Rico, so most travellers go via the US. American Airlines (020-7365 0777; aa.com) is the leading airline to Puerto Rico. It offers frequent connections from Heathrow. Delta (0845 600 950; delta.com) has options from Gatwick, Heathrow and Manchester, and other US airlines can offer alternatives.

The only way to avoid America is to fly on Iberia (0870 609 0500; iberia.com) from Heathrow via Madrid to San Juan. But Puerto Rico's entry requirements are identical to the gruelling procedures for travelling to America, with the need to register at least three days in advance if you plan to visit from 12 January 2009 onwards, and the requirement to be photographed and fingerprinted on arrival.

And get around?

Public transport outside San Juan comprises an unreliable and infrequent network of private minibuses, so you will be better off renting a car. Rates for economy-sized cars with unlimited mileage start at $40-50 (£27-33) per day or $250 (167) for a week, but can escalate dramatically at Christmas/New Year and during the busy July/August period. Budget, Thrifty and Hertz have a presence on the island, but Charlie Car Rental (001 787 728 2418; charliecars.com) is an economical local alternative.

Where can I learn more?

My book, the first Rough Guide to Puerto Rico (£12.99) is published this week. The Puerto Rico Tourism Company (0800 898 920; topuertorico.org) can provide more information.

Holy grounds

The Vatican once ordered coffee exclusively from Puerto Rico, and the island still grows some of the finest Arabica beans in the world.

Its independent gourmet producers maintain a low profile on the international market. Most of them will, however, sell directly from the farm if you call in advance. Of the brands to seek out, try Finca del Seto Café, a rich, nutty brew created on a small plantation north of Jayuya. To buy freshly ground and roasted beans in person, the owners prefer you email beforehand (fincadelseto@aol.com).

For a stronger punch, try Mi Café del Pais, produced by the Nupcay cooperative north of Yauco (001 787 856 4121; nupcay.com). The potent Selección Catador is made with sun-dried beans grown more than 2,600ft above sea level; expect to pay around $8 (£5.30) for 14oz.