ST. JOHN, U.S. Virgin Islands - There is Caribbean luxury travel of the $500-a-night variety: Chocolates on your Frette linen-cased down pillow. A swim-up bar at the infinity pool. The iPod docking stations in your room. And, of course, air-conditioning.

Then there's Caribbean luxury travel that doesn't require a big bank account, and here's what it gets you:

A million-dollar view from an eco-tent in St. John, Virgin Islands, overlooking both the Atlantic and the Caribbean, with no other building in sight.

The sound of rain crashing on the canvas roof at midnight after you've scrambled to zip up the screen windows.

A 3 a.m. moonset in a sky full of winking stars like big, fat diamonds, while tree frogs peep and lightning flickers from a storm out at sea.

A mile hike to snorkel in water as clear as gin, on reefs full of neon-colored fish.

Flopping, exhausted in your bathing suit and T-shirt, into a charming little roadside restaurant shaded by banana trees for a frozen mango daiquiri and a plate of salty crisp fish and chips (the fish caught just a few miles from where you are sitting).

Oh, and something else that no money in the world can buy: the knowledge that you, the visitor, are treading lightly on this paradise, and that after a week of swimming, eating, drinking and sleeping, you will leave the place almost as pristine as you found it.

That's because you showered in solar-heated rainwater collected from that overnight rainstorm, in a permanent structure that evokes not so much a tent as a tree house and that's made with recycled materials, with no air-conditioning but cooled by ocean breezes.

Maybe it's a stretch to call the 51-acre Concordia Estates - named for a sugar plantation that once stood here during the islands' Danish colonial past - a high-end travel experience. That is, unless you buy into the notion that a week spent "roughing it" on one of the last truly unspoiled Caribbean islands, where more than half the island is protected national park, is something of a luxury these days.

Concordia is the brainchild of Stanley Selengut, who founded the legendary Maho Bay camps in 1976 at the beach of the same name on St. John. Maho Bay was one of the first "eco-tourism" venues in the Caribbean, says Selengut, who was trained as a civil engineer, is known as a canny businessman, and who regards himself as a staunch environmentalist.

"I cater to a particular kind of human being who demands a certain kind of experience, people of like minds," Selengut, 81, says by telephone from his home in Bridgehampton, N.Y.

"And the people I'm trying to attract come back all the time, and that makes it profitable."

While Maho Bay has 140 units, Concordia is much smaller, with 38 built on a hillside overlooking the park's gorgeously desolate Ram's Head. Ram's Head is framed by Drunk Bay, which faces east into the Atlantic, and Salt Pond Bay, facing south into the Caribbean.

A half-dozen of the units are wheelchair accessible, Selengut says, and he is building eight more high-end eco units. They aren't tents, but houses, made with "eco-panels" - solid building panels that replace concrete - that tightly insulate the space so that the rooms remain cool in hot weather.

In high season, Concordia has its own restaurant and yoga studio; a well-stocked general store is open year-round. There's also Internet access at Concordia's reception area ($2 for 15 minutes; $7 for an hour). Selengut is looking to continue the popular "Trash to Treasure" program he started at Maho, including a craft center that turns the site's solid waste into art and building materials, and which offers classes in clay work, glassblowing, and other activities.

He acknowledges that the 35 years of human presence at Maho has taken its toll on the reef there, as it has at Trunk Bay and other popular beaches on the island.

At Concordia, the luxury can be found in privacy: Instead of community showers, as at Maho Bay, each tent has a separate area with a compost toilet and solar-heated shower across a small breezeway. There's a small kitchen with two propane burners and a battery-operated refrigerator, and one electric light in each room, but my family squabbled over the one outlet - out of doors - to recharge their various iPods and smartphones.

We visited Concordia in the off-season, early August, which has benefits and trade-offs.

In high season, which begins in November and ends in May, there's that incredible moment when you step off a plane from 28-degree Pennsylvania into 83-degree temperatures and soft trade winds. But you also get high prices, crowds (even in relatively off-the-beaten-path St. John), and, from December to March, high winds, the so-called "Christmas winds," that blow constantly.

In low season, you go from hot (in Pennsylvania, it was above 90 degrees the week we were gone) to slightly less hot (in St. John that same week, temperatures averaged about 87 degrees), made bearable by those constant breezes, less crowded beaches and lower prices.

Did I say lower prices?

For $150 a night for a family of five (in high season, it's about $100 more a night), we slept comfortably in a Concordia eco-tent that included a small deck where we played cards, sipped rum, and gazed at the British Virgin Islands dotting the sea.

Except for that fierce storm the first night, we got very little rain the rest of the week, although July had a record rainfall, turning our usually arid part of the island a lush green.

Far below our deck, in undergrowth, land crabs rustled. The resort encourages you to throw your fruit and vegetable scraps and coffee grounds over the side - the crabs eat it all, and because they're an important part of the island's ecosystem, you are doing good, too.

The National Park Service - which oversees land donated by Laurance Rockefeller in the 1950s - does an admirable job of keeping the beaches clean and beautiful, even with development nearby on what remains of privately owned properties.

Unfortunately, some of the coral reefs have taken a beating. Trunk Bay's much-touted underwater coral reef trail, complete with signs, offered disappointingly few fish. But Leinster Bay and Waterlemon Cay gave us sea turtles, angelfish, and those schools of baby fish that swim by the thousands, in unison, just inches away, without ever touching you.

For a roller-coaster experience, it can be fun to drive on the left side of the road in a jeep - a must if you want to explore the island, although not part of the "eco" experience, given that you get nine miles per gallon. There is a bus ($1 for the ride into St. John's capital, Cruz Bay) that is supposed to come once an hour, but it's not reliable.

Concordia isn't for everyone. If you're not in decent shape, you might find the steps up from your cabin (140 from our unit) to the private road - where cars are parked - taxing. Walkways to other parts of the resort were shaded and attractive.

If you hate the heat (even when there's a breeze), you might find the mornings - when there was less of a breeze and the sun rose over the British Virgin Islands and shone directly into our cabin - uncomfortable. But we managed by driving to one of the island's 39 beaches and immersing ourselves in the cool, turquoise water for a few hours.

Visitors have called their stay at Concordia a "life-changing experience," and indeed, it is, even without air-conditioning.

If that's still not enough, you can stay at one of the island's two high-end, highly manicured resorts, where you can have the chilliest room you want. But it's doubtful you'll feel as close to the island's beating green heart as we did in our cabin, where at night the tree frogs and other jungle animals called to each other - and to us.

Green Vacation

For information about Concordia Estates and Maho Bay Camps, go to www.maho.org or call 1-800-392-9004.

For information about St. John and the U.S. Virgin Islands, go to www.usvitourism.vi or call 1-800-372-8784. EndText