1. ISLA ESPÃSANTO MEXICO
Relaxation Redefined: Guana Island
Twenty miles off Baja's La Paz, this arid, Manhattan-size island in the Sea of Cortez, with its towering cliffs and deeply carved inlets, is home to a third of the world's whale and dolphin species. Though kayakers flock to the island's electric-blue waters, you can always find an empty cove to call your own.
Hideaway: There are no accommodations, but camping is allowed on most beaches.
Exploring: Besides world-class kayaking, there's snorkeling, scuba diving, and fly-fishing for black skipjack and topsail pompano; you may find yourself in the water with sea lion pups or giant manta rays.
The Fine Print: Baja Outdoor Activities (011-52-612-125-5636, www.kayakinbaja.com), in La Paz, runs four- to seven-day guided trips starting at $370 per person.
2. SEABIRD KEY FLORIDA
A five-minute boat ride from Marathon, in the central Florida Keys, this wooded ten-acre island has one old-Florida-style stilt house with lots of decks, a widow's walk, and an eco-conscious setup using solar power and a rainwater-collection system.
Hideaway: The house sleeps eight in two double bedrooms, with private baths on the main level, and four bunks in a sleeping loft. Cook the snapper you catch, or cruise over to Marathon for dinner out.
Exploring: The house comes with a 19-foot runabout, a canoe, kayaks, sailboards, and snorkeling and fishing gear.
The Fine Print: $4,695 per week for up to four people, $350 per additional person; 305-669-0044, www.seabirdkey.com
3. MUSHA CAY BAHAMAS
Rent this entire 150-acre island, in the aqua shallows north of Great Exuma, for yourself and up to 23 of your closest—and luckiest—pals. You'll be doted on by a discreet, sworn-not-to-name-drop (OK, Oprah Winfrey and Tom Hanks have been here), live-in staff of 37.
Hideaway: Of the five guest dwellings, the most lavish is a 10,000-square-foot hilltop English colonial manor house with two bedrooms. The others are brightly painted two- to five-bedroom beachside villas and an ultraprivate thatch-roofed beach house for two. Enjoy multicourse feasts prepared by a world-class chef in the waterfront dining room, the beach bar, or your villa.
Exploring: Play tennis, snorkel, fish for blue marlin, take advantage of a flotilla of speedboats and sailboats, or hop over to Nassau on the resort's Twin Otter (unless, of course, you've brought your own plane).
The Fine Print: Except for two weeks each year when guests can rent an individual house, the island is reserved exclusively for one party at a time; the nightly rate is $24,750 for one to eight guests (all-inclusive), $43,150 for 24 guests; 877-889-1100, www.mushacay.com
4. GUANA ISLAND BRITISH VIRGIN ISLANDS
You'll share this mountainous 850-acre island wildlife preserve, just north of Tortola, with flamingos, screech owls, six-foot iguanas—and a maximum of 30 people.
Hideaway: Fifteen rooms in seven simple stone cottages, most with decks overlooking tranquil Muskmelon Bay, are strung along a ridge. West Indian–style cuisine is served on the terraces of the main house, built on the ruins of an 18th-century sugar plantation.
Exploring: Miles of hiking trails lead to lookouts and empty ivory beaches. You can circumnavigate the island by kayak, search for black-necked stilts, sail small boats, and snorkel the reefs off White Bay beach.
The Fine Print: Doubles, $895, including all meals; rent the island for $15,500 per night; 914-967-6050, www.guana.com
5. PETIT ST. VINCENT GRENADINES
After the golf-cart ride from the dock to your cottage, you may not see another soul during your stay on this hilly 113-acre island, 40 miles south of St. Vincent—if that's how you want it. Need something? Hoist a yellow flag on your personal bamboo flagpole. If you want to be left alone, fly the red one.
Hideaway: Twenty-two airy stone cottages with terra-cotta floors and private sundecks are tucked in the palms along, and above, a sugary two-mile strand. Dishes like spicy tannia-root soup and grilled local snapper are served in the stone-and-timber dining pavilion, in your cottage, or in one of the many thatched palapa huts dotting the island.
Exploring: Help yourself to glass-bottom kayaks, sailboards, and catamarans. Hike through banyans and rubber trees to the top of 275-foot Marni Hill, where a lone hammock—and killer views—await. Larger yachts and sportfishing boats can be chartered for daylong fishing or scuba-diving trips.
The Fine Print: Doubles, $585–$910, including meals; for two weeks each year, rent the island for $12,870 per night; 800-654-9326, www.psvresort.com
6. ISLAS SECAS PANAMA
In the little-visited Las Secas archipelago, off Panama's Pacific coast, lies lush Isla Cavada, a ladle-shaped 1,000-acre enclave with jagged cliffs and waterfalls that's home to a one-year-old, low-impact resort for just 12 guests.
Hideaway: Stay in one of six secluded, cove-front, canvas-sided casitas, each with a queen bed and full bath. Dine on seafood specialties, including the superb ceviche de corvina—raw white sea bass marinated in lime juice—in the open-air cocina, or in your casita.
Exploring: Deep-sea fish for giant black marlin and tuna; scuba-dive among sharks, dolphins, and 400-pound jewfish; search for humpback whales; or surf the epic barrels at Morro Negrito, a 12-mile boat ride away.
The Fine Print: Doubles, $600 (four-night minimum), including all meals and some activities; 805-729-2737, www.islassecas.com
7. WILSON ISLAND AUSTRALIA
Just north of the Tropic of Capricorn and a 40-minute boat ride from Heron Island, this coral platter in Great Barrier Reef Marine Park welcomes only 12 guests at a time.
Hideaway: Six permanent tented cabanas with raised wooden floors offer king beds, battery-operated lamps, and water views. Simple meals of fresh fish and local fruit are served family-style in the community tent.
Exploring: The emphasis is on appreciating the fragile environment, with snorkeling, birdwatching, and, from December to April, guided walks to view the hatching of green and loggerhead turtles.
The Fine Print: The five-night Wilson Island Experience ($1,425 per person) includes two nights on Heron Island and three nights on Wilson Island, all meals included; 800-225-9849, www.wilsonisland.com
8. DOLPHIN ISLAND FIJI
A ten-minute cruise from the north end of the Viti Levu mainland, this nine-acre coral islet hosts just two couples at a time. Hideaway: A pair of elevated, open-to-the-breezes bures are decorated Fiji-style with tapa cloth and lashed beams. One has two double suites for sleeping; the other is where chefs work magic: Think papaya, mud crabs cooked in coconut milk, and poisson cru. Exploring: Kayak around the island, look for clownfish on the reefs, sail a Hobie Cat, and scuba-dive sites like Dream Maker, where sheer walls sport multihued soft corals.
The Fine Print: $1,540 per night for two, $1,940 for four (four-night minimum); 011-64-7-378-5791, www.dolphinislandfiji.com
9. MOTU HAAPITI RAHI BORA BORA
A nearly perfect circle of coconut palms and white sand, this islet in the coral barrier reef encircling Bora Bora is only big enough for two houses—the owner's and a three-bedroom cottage that holds up to five guests. Hideaway: Decorated with traditional bamboo furnishings, the solar-powered house sits on stilts just 15 feet from the clear lagoon. Buy groceries en route to the island, and cook at home.
Exploring: Kayaks, fins, and masks are at your disposal; the snorkeling—look for eagle rays and giant wrasses—is superb. Buzz over to Bora Bora by motorboat for scuba diving, water-skiing, and horseback riding.
The Fine Print: Rent the house for $550 per night; 011-689-74-24-73, www.private-island.net