Molten sunsets and a dozen beach bars, including Mr. X's Shiggidy Shack, make Frigate Bay, just two miles southeast of Basseterre, the liveliest place on St. Kitts. A construction project has degraded South Friar's Bay, but good, uncrowded beaches scallop the remaining shoreline of the Southeast Peninsula. Turtle Beach has the most services, while Cockleshell Bay is notable for Lion Rock Beach Bar, whose Rasta owner dispenses rum punch and BBQ (869-663-8711). Anchored by Four Seasons Resort Nevis, two-mile-long Pinney's Beach features the finest sand, the calmest water, and, in Double Deuce and Sunshine's, the best distractions. Further north, a prevailing northeast breeze attracts windsurfers to Oualie Beach, while thickets of sea grape afford Lover's Beach visitors plenty of privacy. But whatever you do as you woo, remember the beach is on final approach for planes landing at Nevis's airport.

Begun by the British in 1690 to deter other colonial contenders, this landmark stone fortress is the only man-made UNESCO World Heritage site in the eastern Caribbean. A superb military design and ingenious engineering embellish its dramatic setting atop an 800-foot mount on the island's west coast, which also speaks volumes about the talent and tenacity of the countless slave workers who built the "Gibraltar of the Caribbean.'' From the cannon-lined bastions, commanding views extend all the way north to St. Eustacia and Saba. Inside the citadel, Fort George Museum provides a concise history of the island and its European settlement, slavery, and sugar industry.

Open daily from 9:30 am to 5:30 pm.

There are more than 70 dive sites, including dozens of unexplored shipwrecks, around Nevis and St. Kitts; most of them require a short boat ride and have visibility of 60 to 100 feet. The area may not be a diving mecca, like the Cayman Islands or Belize, but it's worth excursions to the Grid Iron in the Nevis–St. Kitts channel or the River Taw Wreck. You're likely to see stingrays, colorful reef fish, and nurse sharks. Both Pro-Divers, at Fisherman's Wharf on St. Kitts, and Scuba Safaris, at Nevis's Oualie Beach, are PADI-certified shops. Also at Oualie, you'll find Under the Sea, where marine biologist Barbara Whitman runs guided snorkeling trips from a dinghy (à la Jacques Cousteau), rents sea kayaks, and offers a kid-friendly crash course in underwater ecosystems.

St. Kitts hosts a music festival every June, which draws a wide array of international headliners (Chaka Khan, Maxi Priest, and Michael Bolton have all performed here) as well as Caribbean icons such as Burning Spear. The island throws its annual Carnival party over Christmas and New Year's (www.stkittscarnival.com). In late July, Nevis's blowout event, Culturama, celebrates the emancipation of the slaves in the 1830s with a week of street fairs, beauty contests, and live-music "jump-ups" (www.nevisculturama.net). A new annual October event is the Nevis International Culinary Heritage Exposition, or NICHE, where top Caribbean chefs offer demos, dinners, and seminars, and the wine flows liberally (www.nevis-niche.com).

The abundance of dorado, kingfish, barracuda, tuna, snapper, mahimahi, and wahoo in these waters attracts a lot of avid anglers. The annual Nevis Yacht Club Sports Fishing Tournament takes place each October, and some people have even dropped old car bodies into the ocean to create reefs. Charters such as Nevis Water Sports include an open bar, which nearly guarantees some good fish tales (Oualie Beach; 869-469-9060; www.fishnevis.com).

Unlike the pancake-flat islands of the Bahamas and Turks & Caicos, Nevis and St. Kitts have real hills and mountains, and hiking away those piña colada calories on an early-morning trek feels oh-so-good. (Be back before the midday sun.) You might want a guide so you don't end up in your own episode of Lost. On St. Kitts, follow Earl "the Duke of Earl" Vanlow up to the milewide crater rim of Mount Liamuiga, the 3,792-foot volcano that formed the island (869-465-1899). On Nevis, Lynnell Liburd, an eco expert based in the village of Hardtimes, will guide you to Nevis Peak, a 3,232-foot volcano. Along the way, Lynnell passes along tidbits of ethnobotany—who knew stinging nettles could relieve cramps?—and points out the Green Vervet monkeys (869-469-2758). There are also more gentle (and do-it-yourself) nature hikes around Nevis's Golden Rock Estate and the Gingerland district.

The Guilbert family raised Arabian show horses for 25 years in California before relocating to Nevis, where they now run the Nevis Equestrian Centre, which trots riders along beaches, past plantations and churches, and through coconut groves. Trinity Stables on St. Kitts, meanwhile, offers half-day tours through mountainous sections of the rain forest.

Many of the former sugarcane roads, some 200 of them, are now perfect trails for mountain biking. They're mostly long loops of doubletrack, so beginners and intermediates should feel comfortable, although the heat and hills (plus some hidden singletrack) can challenge even knobby-tire experts. To rent equipment or hook onto a good guide, check out the Wheel World cycle shop, on Oualie Beach. It's owned by a former Shakespearean actor, Winston Crooke, who now spends his time pursuing his twin loves of biking and windsurfing (869-469-9682; www.bikenevis.com).

Staged every March, this multisport race sends top international athletes on a swim through Gallows Bay, a bike ride out to the airport, and a run back into Charlestown. Participants should be prepared for the heat, which often hits the high 80s. Register at www.neviscycleclub.com.

St. Kitts has the livelier nightlife of the two islands, much of it centered in the Frigate Bay area. Tiger's, at the Marriott, sometimes roars (869-466-1200), while the Shiggidy Shack has bonfires on the beach, a firedancer, and live music (869-762-3983). The nearby Monkey Bar is also usually swinging (869-465-8050).

On Nevis, you'll find après-dinner action at Tequila Sheila's Cades Bay (869-469-8139), Double Deuce on Pinney's Beach (869-469-2222), or in downtown Charlestown at V's Courtyard (869-665-1801).

Captain Les Windley—a quintessential salty dog—runs Sea Nevis Charters from Nevis. Book a day-sail charter on his 44-foot sloop, Sea Dreamer, which is stocked with snorkeling equipment and beer. You can also rent Hobies (a small type of catamaran) on Oualie Beach. Leeward Island Charters offers catamaran excursions from both islands.

A lot of tourists like to windsurf between the islands, and though the winds off Nevis can froth up to wave-jumping conditions, they're generally calm enough to create an excellent learning spot for beginners. Need equipment or lessons? Turn to the resident sportsman-about-town, Winston Crooke (see Mountain Biking). His shop is on Oualie Beach (869-469-9682; www.bikenevis.com).

Downward dog, beachside? Private yoga and pilates sessions on Nevis can be arranged with instructor Nikki Johnson (869-663-9850). The Four Seasons also offers sessions at its Sports Pavilion.