If it's aquatic, St. Maarten/St. Martin offers it: from sailing to scuba diving, big game fishing to boogie boarding. It almost seems the island has more marinas per square mile than anywhere else on earth (one even changed its name to Dock Maarten, neatly combining two local economic mainstays -- boating and shopping). Land-based excursions are less popular, though hiking and mountain biking can be rewarding.

Boating

Day rentals are available from Lagoon Sailboat Rental in Simpson Bay Lagoon (tel. 599/557-0714; www.lagoonsailboatrental.com). You can explore the lagoon -- the largest in the Caribbean -- and surrounding waters in state-of-the-art 6m (20-ft.) Sunfasts for $150 for a full day ($110 for a half-day). The congenial Cary and company also give a thorough 10-hour course for $200 (for 2-3 people) that can be broken up however you like.

Come Sail Away -- Ever dreamed of racing a state-of-the-art yacht? You can -- and no previous sailing experience is necessary -- when you sign on to crew aboard one of five famed America's Cup yachts in the St. Maarten 12-Metre Challenge in Philipsburg at Bobby's Marina (tel. 599/542-0045; www.12metre.com). Among the prestigious yachts are Dennis Conner's champion Stars & Stripes, True North, and Canada II. Each boat takes 9 to 18 sailors (12 and up) for a 3-hour race ($80-$100 per person). It's great fun and thrilling sailing: The captains and mates brief their swabs-for-a-day on the basics, from grinding a winch to tacking. Celebrate your win (or just finishing) with a complimentary rum punch.

Deep-Sea Fishing

The island hosts several highly regarded competitions, including March's Marlin Cup and June's Billfish Tournament, that lure an impressive international roster of entrants. The waters teem with tuna, wahoo, snapper, grouper, jack, pompano, yellowtail, marlin, and other big game fish. The crew from Lee's Roadside Grill on Welfare Road 84, Simpson Bay (tel. 599/544-4233; www.leesfish.com) knows where to catch the big boys, since they supply their own wildly popular seafood haunt. Charter one of its 9.3m (31-ft.) Bertrams for a half-, 3/4-, or full-day excursion with a minimum of four people (maximum six). Drinks are included in the half-day trip ($150 per person) and lunch and drinks are included in the 3/4- and full-day excursions ($200 and $250 per person respectively). And yes, they'll cook your trophy up at the restaurant for no extra cost.

Pelican Watersports, on the Dutch side, at the Pelican Resort Club, Simpson Bay (tel. 599/54-42640), has boats available for deep-sea-fishing expeditions priced at $150 per person for a half-day (7:30-11:30am) or $300 per person for a full-day (7:30am-3pm) excursion. In high season, reservations must be made 1 week in advance.

Golf

The Mullet Bay Golf Course (tel. 599/545-2850) is the island's only golf course. It's a battered 18-hole Joseph Lee-designed course whose fate has hung in the balance, based on ongoing court battles, for years. The ruins of the Mullet Bay resort surround the course. The island's flagship resort was severely damaged by Hurricane Luis in 1995, and no one has ever gotten around to cleaning up the mess (more to the point: no one will take financial responsibility for the cleanup, not even its zillionaire developers). But golfers find their way here anyway and putter along on the lumpy, poorly kempt course. Greens fees are $50 for 9 holes or $80 for 18 holes; rental carts are $50.

Hiking & Mountain Biking

Despite its small size, the island offers terrain ranging from limestone plateaus to a central volcanic ridge topped by 445m (1,482-ft.) Pic du Paradis, and ecosystems from semi-desert to tropical rainforest. Birders will sight coots, black-necked stilts, and ospreys nesting amid the swamps and cliffs.

Adrenaline junkies and eco-buffs will feel at home at TriSport headquarters on 14B Airport Rd. in Simpson Bay (tel. 599/545-4384; www.trisportsxm.com). Bikers can rent Trek mountain bikes and hybrids ($17 half-day, $24 full day, $110 per week) -- TriSport will deliver the bikes to your hotel for a $20 fee. TriSports also ventures into the open water with snorkeling/kayaking tours around Anse Guichard's hulking Henry Moore-ish boulders and Caye Verte. The 2 1/2-hour Simpson Bay Lagoon tour ($49) includes instruction and a stop at deserted Grand Îlet, whose mangrove system houses unusual critters from sea cucumbers to upside-down jellies. You can rent kayaks for $15 per hour; a double kayak costs $19/hr.

Horseback Riding

In Seaside Nature Park, Lucky Stables (tel. 599/544-5255; http://luckystables.shoreadventures.net) offers a daily romantic Sunset Champagne ride ($72 per person) including a marshmallow roast or a beach and trail jaunt (from $48) into secluded, stony, unspoiled Cay Bay (aka Cape Bay) as Saba, Statia, St. Kitts, and Nevis drift on the horizon. Guides explain local folklore, fauna, and flora along the picturesque route through the closest thing to wilderness on the Dutch side. Horseback-riding lessons for adults and children are also offered in Seaside Park's Olympic-size riding ring ($20/lesson; $120 12-lesson card) Barring heavy traffic, the stables are 10 minutes from the airport and 15 minutes from Philipsburg. Its counterpart on the French side is the Bayside Riding Club, Rue de Le Galion, Coconut Grove, St. Martin (tel. 590/87-36-64; www.baysideridingclub.com). Beach rides are a highlight ($95 1-hr. private ride, $70 1-hr. group ride).

Scuba Diving

Although the nearby island of Saba is considered to be the area's top dive sight, the scuba diving is quite good around St. Martin, with reef, wreck, night, cave, and drift diving; the depth of dives is 6 to 21m (20-69 ft.). Off the northeastern coast on the French side, dive sites include Ilet Pinel, for shallow diving; Green Key, a barrier reef; and Tintamarre, for sheltered coves and geologic faults. To the north, Anse Marcel and neighboring Anguilla are good choices. The waters around St. Maarten offer good dive wrecks, including the 1770 British man-of-war, HMS Proselyte, which came to a watery grave on a reef 2km (1 1/4 miles) off Philipsburg in 1801. Most of the big resorts have facilities for scuba diving and can provide information about underwater tours, photography, and night diving.

LeRoy French, the larger-than-life owner of the island's oldest dive shop, Ocean Explorers, at Kim Sha Beach (tel. 599/544-5252; www.stmaartendiving.com), is still diving more than a half-century after he caught the bug (using some of Cousteau's first Aqua Lungs). Starry students in his 40-plus-year career have included Jackson Browne, Matthew McConaughey, and Sandra Bullock. He's been profiled by Sports Illustrated, and even the Cousteau team might envy his vivid videos. The personalized touch -- he takes a maximum of six divers -- costs a bit more ($53-$59 single-tank dive, $98-$104 double-tank) and means reservations are essential. Ocean Explorers also offers day trips ($90-$115) to the island of Saba, considered to be the area's premier dive site.

One of the island's premier dive operations is Scuba Fun, whose dive center is at the Great Bay Marina, Dock Maarten, Philipsburg (tel. 599/54-23966; www.scubafun.com). It offers morning and afternoon dives in deep and shallow water, wreck dives, and reef dives. A resort course for first-time divers with reasonable swimming skills costs 75€ and includes instruction in shallow water and a one-tank dive above a coral reef. A morning two-tank dive (certified divers only) costs 85€.

Another recommended dive operation is Octopus Diving (tel. 590/29-11-27; www.octopusdiving.com), in Grand Case. Its multinational staff provides PADI courses, night dives, and underwater photography to some 30 dive sites around the island. One-site dives go for $99, and two-site dives for $85 to $99, all equipment included. Dive Safaris, at Simpson Bay (tel. 599/545-2401; www.divestmaarten.com) -- offers competitive rates and a full range of PADI certification courses, including specialty instruction in marine habitats, photography, and wreck diving. Those wanting to get up close and personal with sharks can don chain-mail-like armor to feed the sharks in their "Shark Awareness Dives" ($80 per person). Rates are $50 to $55 for single-tank dives; $95 to $100 for double-tank dives; and $75 for night dives.

Snorkeling 

The calm waters ringing the island's shallow reefs and tiny coves make it a snorkeler's heaven. The waters off the northeastern shores of French St. Martin have been classified as a regional underwater nature reserve, Réserve Sous-Marine Régionale, which protects the area around Flat Island (also known as Tintamarre), Ilet Pinel, Green Key, Proselyte, and Petite Clef. Equipment can be rented at almost any hotel, and most beaches have watersports kiosks.

Eagle Tours at Bobby's Marina in Philipsburg (tel. 599/543-0068 or 599/542-3323; www.sailingsxm.com) offers snorkeling, kayaking, lagoon sailing, and sightseeing tours aboard its fleet of seaworthy vessels. The 23m (76-ft.), custom-designed Golden Eagle catamaran (originally built for the prestigious Whitbread Around the World Race) cruises to various deserted strands and cays for snorkeling and soaking up both tropical ambience and drinks (the pampering service includes a floating bar -- you will be dancing or leading a conga line by the end of the trip). The flatboat Explorer stops in Marigot for shopping before heading home; mimosas and rum punches flow copiously. The Friday jaunt ($99 per person) sails to Tintamarre and Creole Rock, puts in at Grand Case for lunch, then stops by Baie Longue for a final cooling dip. Transportation to and from your hotel is included.

Both Scuba Fun and Octopus Diving provide guided snorkeling trips to the island's teeming offshore reefs. Snorkeling trips with Scuba Fun cost 30€ for a half-day, plus 7.50€ for equipment rental. Snorkeling trips to two sites with Octopus Diving cost $40 (including all equipment).

Tennis

You can try the courts at most of the large resorts, but you must call first for a reservation. Preference, of course, is given to hotel guests.

Water-Skiing & Parasailing

Most of French St. Martin's large beachfront hotels maintain facilities for water-skiing and parasailing, often from kiosks that operate on the beach.

Club Caraïbes at the Hôtel Mercure Simson Beach in Nettle Bay (tel. 690/33-30-01; www.skicaraibes.net) provides wakeboard and jet ski rentals, as well as water-skiing instruction with Laurent Guy and Brigitte Lethem (the 2004 U.S. Master Champion). You can learn slalom or tricks for 40€ per set; 5-day intensive water-skiing and wakeboard courses cost 350€ to 720€, depending on the season.

Windsurfing

Most windsurfers gravitate to the eastern part of the island, most notably Coconut Grove/Le Galion Beach, Orient Beach, and, to a lesser extent, Dawn Beach, all in French St. Martin. The top outfitter here, Tropical Wave, Le Galion Beach, Baie de l'Embouchure (tel. 590/87-37-25; www.sxm-orientbeach.com/chezpat), capitalizes on the near-ideal combination of wind and calm waters. Pat rents Mistrals for 20€ an hour, with instruction offered at 30€ an hour, and 45€ for a 2-hour beginner course. They also rent snorkeling gear, pedal boats, and kayaks (tours can be arranged).

Wind-Adventures (formerly Club Nathalie Simon), on Orient Beach (tel. 590/29-41-57; www.wind-adventures.com), is one of the Caribbean's premier windsurfing schools. Lessons cost 120€ for 1- to 3-hours of instruction. Kite trips for the experienced to Green Cay start at 95€. Wind-Adventures also rents windsurfers and Hobie Cats and offers both safaris and instruction (with excellent multi-lesson discounts).

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.