Welcome, Sierra Club members! Chumbe's seven bungalows, outfitted with solar-heated showers, are fit for Robinson Crusoe. The lodge was founded in conjunction with Zanzibar's first marine park and now trains local rangers. Spot the rare nine-pound coconut crab, the largest on land, then snorkel with dolphins and hawksbill turtles.
+ Doubles from $400; chumbeisland.com

Concordia's solar-powered tents are decidedly rustic (yup, composting toilets), but their location on St. John’s is five-star, set on a hillside next to Virgin Islands National Park. Snorkeling and scuba diving are de rigueur, as is a visit to Maho Bay's Trash to Treasures, where guests make art from recycled glass.
+ Doubles from $105; maho.org

Located east of Palau, the jumble of steep jade mountains known as Kosrae Island is farther than most tourists venture. That's why Kosrae Village, the island's one and only ecolodge, feels like such an authentic slice of South Pacific life. Dive for a coral-monitoring project, learn to weave at a local village, and dine on coconut-smoked wahoo.
+ Doubles from $149; kosraevillage.com

Nihiwatu has a consistent break right off its 1.5-mile beach, but this chilled-out surf nirvana attracts more than pro riders. Join the active devotees of this coconut-biodiesel-fueled resort for yoga in the thatch pavilion, find bliss in the spa, and mountain bike to remote villages. Thanks in part to the resort, thousands of villagers now have access to clean water and health clinics.
+ Doubles from $440; nihiwatu.com

Staying at Ranweli's tiled bungalows, modeled after a traditional village, is just short of complete Sri Lankan immersion. Locals demonstrate weaving and cooking techniques, an on-site fruit stall sells medicinal drinks, and an ayurvedic center offers herbal oil massages—all just a two-hour drive from the capital.
+ Doubles from $60; ranweli.com

Instead of white sand and palms, the Caribbean isle of Dominica is covered in volcanoes and virgin jungle. A15-minute hike into the vines and heliconia, Rosalie's tree houses and cabins feature wind-powered lights and rainwater showers. After waterfall hikes, eat an organic dinner with Brit owner Jem Winston, a London taxi driver turned sustainable-living guru.
+ Doubles from $50; rosalieforest.com

"No news, no shoes," is the resident philosophy at Soneva Fushi, which is to say: Kick back. Dive or windsurf the baby blue waters, take a wine-tasting tutorial with the sommelier, or dine on your own private beach. Behind its elegant facade, this 65-suite resort has committed to zero carbon emissions by 2010 with innovations like deep-ocean water cooling.
+ Doubles from $749; soneva.com

While hoteliers have jostled for elbow room on Caribbean beaches since the 1950s, remote South Andros Island has remained blissfully development free. To preserve the pristine area, Tiamo’s owners hid their 11 airy wooden bungalows in the jungle and built a field of solar panels to power them. Cast for bonefish in world-renowned flats or snorkel one of the planet’s largest reefs.
+ Doubles from $630; tiamoresorts.com

Vamizi Island, in the Quirimbas Archipelago, is the prototypical white-sand-and-palms paradise, but the real attraction at this ten-villa resort lies in the water: Explore some of the world’s most pristine coral reefs, sail on locally made dhows, then head offshore to search for migrating whales.
+ Doubles from $900; vamizi.com

While taking in uninterrupted views of the turquoise sea from a villa handcrafted by local Seychellois carpenters, it's easy to mistake this as one's own private island. It's even harder to believe that the isle was once ravaged by invasive species. African outfitter Wilderness Safaris rehabbed the land by reintroducing endemic tortoises, birds, and plants and building 11 no-expense-spared villas, a spa, and a dive center.
+ Doubles from $5,000; north-island.com