Ask not what nature can do for you but what you can do for nature -- and humanity, as long as you're feeling virtuous. That's the premise behind ecotourism, arguably the era's fastest-growing travel trend. While the concept is still too new to maintain a single definition, most agree on ecotourism's basic tenets set forth by The International Ecotourism Society: minimize environmental impact; build cultural awareness; provide positive experiences for both visitors and hosts; yield direct financial benefits for conservation and the local population; and raise sensitivity toward host countries' political, environmental, and social climate. It's a tall -- but not insurmountable -- order, especially now that eco-tour operators (and eco-lodges to match) are popping up in all corners of the globe. These five destinations represent a mere sampling of what the planet has to offer.

Vanua Levu, Fiji
For decades, Vanua Levu's idyllic palm-fringed beaches have attracted scores of honeymooners; its rugged interior, mountain bikers and hikers; and its vivid coral reefs and even brighter fish, divers. Yet this slice of the South Pacific (and Fiji's second largest island) remains pleasantly unpopulated and a true getaway in every sense of the word.

How it's eco Managed by the owners of the eco-chic Post Ranch Inn in California, the Jean-Michel Cousteau Fiji Islands Resort on Savusavu Bay resembles a traditional Fijian village. Scattered around 17 acres of coconut plantations, 25 thatched bungalows make use of natural ventilation, with floor-to-ceiling slatted windows that open to either the crystal-clear bay or a lush tropical garden. Activities abound, from snorkeling excursions accompanied by the resident marine biologist (they claim to be the only Fijian resort to employ one) to planting mangrove seedlings to help preserve the ecosystem.

Don't miss A 20-minute boat ride from the resort, Namena is reputedly one of the 10 best dive and snorkel sites in the world. Marine-life lovers come for its 10-mile-long barrier reef and all manner and size of fish, not to mention one of the largest endangered hawksbill turtle nesting areas.

Details 800-246-3454, fijiresort.com

Kerala, India
The picture of fecundity, this emerald- green state on India's southwest coast has long welcomed the influx of international spice traders -- and the ensuing cultural jumble. To this day, traditional Dutch homes, Chinese fishing nets, and Sephardic synagogues remain the capital's most iconic sights. Ecotourists are starting to outnumber traders, though, thanks to the high concentration of wildlife sanctuaries (14) and the profusion of Ayurvedic-friendly herbs and medicinal plants, which are turning the region into an all-natural holistic haven.

How it's eco With 59 luxe resorts all around India, the gilded Taj Hotel group defies the green stereotype. Below some of its impeccably lacquered surfaces lie solar heating, tracts of land where guests can plant trees, and EcoTaj, a program that last year had employees spending as many as 300,000 volunteer hours teaching marketable skills to indigent communities. Only four of the seven Taj properties in Kerala have the eco-amenities, but each will customize your Indian adventure by arranging excursions like jungle treks, spice plantation tours, and bird-watching safaris.

Don't miss India's answer to bayous, the renowned maze of backwaters is best experienced on the front end of a 100-foot open-air wooden houseboat. Palms stand shoulder to shoulder, breaking formation for the occasional stilted house on the rivers' banks. The real action takes place in the water -- children play, men fish, and the rare Siberian crane does both.

Details 866-969-1825, tajhotels.com

The Bolivian Highlands and Amazon
Bolivia is known for its coca growers, populist politicians, and bowler-hat-topped women, but the country's pristine natural habitat is quickly taking center stage. The star performers are the lung-challenging Lake Titicaca (at an altitude of 12,500 feet, it's the highest navigable lake in the world) and the 4.5-million-acre Madidi National Park, at the heart of one of the world's richest biodiversity hotspots.

How it's eco Offering 10-day trips into the jungle from May to October, Wildland Adventures prides itself on arranging stays at some of the country's best eco-lodges. La Estancia, located atop Isla del Sol, the mythic birthplace of the Incas, has solar energy power, organic gardens, and unparalleled views of Titicaca. Chalalan Ecolodge, on the other hand, is a cluster of thatch-roofed bungalows surrounded by a lush rain forest and accessible only by dugout canoe.

Don't miss The excursion to San Jose de Uchupiamonas is a bit of a digression from the standard Wildland itinerary (the trip involves a three-hour boat ride and an overnight stay in a barebones guesthouse), but seeing Quechua-Tacana culture up close and personal makes the trek well worth your while. The locals will likely throw a soiree in your honor. And while prospective dance partners don't like to take no for an answer, feel free to pass on the communal coca-leaf cigarettes.

Details 800-345-4453, wildland.com

Bhutan
A study in state-sponsored ecotourism, this little Buddhist kingdom assiduously preserves its ecology and culture. The fact that foreigners were essentially barred until the 1970s hasn't hurt: With nearby Nepal as a cautionary tale in overexposure (think: backpacker pizza joints), Bhutan has limited travel by tacking on a steep visitor tariff. The result is an alternate reality that blends a phallus-wielding patron saint; clans of robed businessmen (pants are a finable offense during formal occasions); and Himalayan passes that qualify as religious experiences.

How it's eco Wind Horse Tours, a Bhutan- and Minneapolis-based business, minimizes impact in several ways, the most important being group size (typically, there's an eight-person cap). Scheduled trips, usually 10 to 14 nights, depart throughout the year. Knowledgeable local guides guarantee authenticity and access -- expect visits to private homes, trekking in the Himalayan outback, and modest but perfectly comfortable hotels.

Don't miss Take a 90-minute hike to reach Taktsang, the physics-defying monastery built into a cliff 4,000 feet above the fertile Paro Valley. Guru Padmasambhava is said to have landed here after flying on a tiger's back from Tibet around 850 A.D., when mythological anti-Buddhist demons threatened Bhutan. Needless to say, the good guru prevailed.

Details 888-834-6773, windhorsetours.com

Laos and Cambodia
Enchanting blends of waterfalls, jungles, and rice paddies, Laos and Cambodia have remained relatively off the beaten tourist path. Ancient Cambodian temples still draw pilgrims as they have for hundreds of years, while Laotian locals line up at sunrise to offer rice to the silent monks on parade. Both countries are recovering from years of internal strife and as a result offer a more authentic and uncharted adventure than their more well-trodden Southeast Asian neighbors. Even UNESCO wants to preserve their cultural treasures: The towns of Luang Prabang in Laos and Cambodia's Angkor are considered World Heritage Sites.

How it's eco Technically, Myths and Mountains is based in Nevada. But with a founder and president who has spent the last 20 years traveling around Southeast Asia, the group might as well be located on the banks of the Mekong River. The company is adamant about giving back to host communities. Chief among its philanthropic efforts is READ (Rural Education and Development), a nonprofit that builds schools, gives scholarships, and trains librarians.

Don't miss Cambodia's Ta Prohm temple is enveloped by the massive roots and branches of strangler figs that span the frail stone buildings. Phnom Bakheng should be viewed from afar; too much wear and tear has left the temple in danger of collapse.

Details 800-670-6984, mythsandmountains.com

Contributing Editor Abbie Kozolchyk lives in Manhattan with her husband.