For someone who loves being outdoors, hopes to drop a couple of pounds or ramp up a fitness routine, and wants to really get away from it all, the Island Experience, a Portuguese-accented boot camp 68 miles south of Rio de Janeiro, delivers a unique riff on the adventure-spa concept. The weeklong program, which promises to "detox your body and de-stress your mind," brackets a rigorous regimen of hiking and kayaking with sunup and sundown yoga classes, plus a daily massage. A low-cal diet capitalizes on luscious tropical fruits and fresh vegetables. Seven days of alfresco adventure play out against the verdant forests and crescent beaches of Ilha Grande (that's Portuguese for "big island"), a sleepy tourist backwater from March to December, when the Island Experience program is offered. (It ceases operation during the hot, rainy Brazilian summer, our winter.)

Why fly 5,000 miles on a $1,000 ticket, and go to the trouble and expense of obtaining a visa, when you could find an adventure spa much closer to home? I went because I was curious to see if this South American innovator had solved my perpetual spa dilemma: Am I willing to sacrifice a precious vacation week that could be spent exploring a new part of the globe to enter the cloistered world of a spa? Moreover, jangled by a fast approaching deadline on my first book and looking to lose the eight pounds I gained while recuperating from a car accident three months earlier, I was an eager customer for de-stress, detox, and a low-calorie diet.

At the risk of spoiling the punch line, I'll say right away that I left the lodge a satisfied client. On my final day on Ilha Grande, as I jackknife into downward dog in a morning yoga class held on a pier, feeling the sun on my skin and a sweet breeze ruffling my hair, I know this experience has been worth every dollar and every mile. Not only have I nourished my body with small meals and supersized servings of exercise; I have actually visited another culture.

The Island Experience was born two years ago when three employees at Body and Soul, another adventure spa on Ilha Grande, thought they had a better concept. "We wanted to keep the active outdoor elements but broaden the mix by introducing guests to the island's history and culture, too," co-owner Steve Haas tells me. A former web designer from San Francisco, Haas spent a week with Martin Marpegan, a lawyer and MBA from Buenos Aires, and Adriana Porchat, a São Paulo native who studied nutrition at the University of California-Davis, hiking the perimeter of the 119-square-mile island to find the prettiest secluded beaches and most scenic rain-forest trails, and hammering out the details of their spa program.

Even during a sold-out week, the atmosphere is intimate--ten people, max--but a flurry of last-minute cancellations reduces this week's guest list to just three. As the boat roars across the bay toward the lodge, we eye one another nervously, wondering if the group is a little too small. Kjerstin, who's 22, dropped out of college two years ago to launch a nonprofit organization that trains college students to work in African refugee camps. She's just back from Zambia, and the Island Experience is a gift from her mom to help her unwind. Jean, a 28-year-old medical-equipment sales rep from North Carolina, is here to rethink her career. Jean has a pet frog at home that eats out of her hand, and after watching her befriend the island's extensive population of pint-size dogs, Kjerstin and I cast our votes for veterinary school. Call us the odd couple plus one: a visionary vagabond, a hardworking new homeowner, and somebody old enough to be their mom. But our circle isn't uncomfortably tight since Martin, Steve, Adriana, and their staff act more like buddies than guides in the following days as they lead us across the water and through the forest, chatting about their lives and this beautiful island.

The boat docks below a trio of buildings that peek out of dense vegetation and overlook a broad bay on the leeward side of the island. Our rooms don't earn any style points--paneled in henna-hued local hardwood, each contains a small wardrobe, a bed with end tables, and a mini refrigerator stocked with bottled water. But the $1.98 decor comes with million-dollar views. French doors lead to balconies overlooking the water: To the left lies a broad sweep of beach, and in the distance, the hilly coast of mainland Brazil shimmers in a bluish haze. On clear evenings, a waxing moon paints a glowing path across the bay. Before I unpack, I throw open the doors and never shut them until I leave for home.

Back at the main building, Adriana hands us ginger-melon smoothies and describes the meal plan: no caffeine, no sugar, no alcohol, and a

mainly vegetarian menu of 1,500 calories a day. (Fish is served two or three times a week.) "We delete all the artificial ingredients, so there are no toxins coming into your body; then we serve foods that cleanse your system, like fruit," she says. "The exercise helps, too: Sweating and the increased circulatory rate help to release the toxins from the body."

It's late September, a time of unsettled weather. I've been lured by average high temperatures around 80 and lows in the upper 60s; now I'm hoping rain won't wash away our fun. The sun breaks through just in time for our first kayak trip and, for the rest of the week, always shines when we're kayaking or sunbathing; it rains mainly at night. Martin tells me that the weather is best March through May, when the temperatures are similarly balmy and the skies are nothing but blue.

On our first morning, we launch kayaks from our home beach and paddle along the coast to lay claim to a pretty little scallop of sand where we sunbathe and swim for an hour before hiking back to the lodge. This establishes the pattern for our days. We're awakened at six for yoga class, then have a light breakfast of cereal and fruit. By eight-thirty we're on the trail or in the boats, kayaking a mile or two, then hiking four or five, with restorative bouts of beach time mixed in. When we get back to the lodge in the late afternoon, there's a relaxing yoga class and massage before dinner. After that, we tumble into bed, basking in the virtuous exhaustion of the well-exercised. Seldom have I brought so many books and read so few. Halfway through the week, Jean asks Martin if we're the most boring group they've ever hosted. "No," he tells us. "Everybody goes to bed at nine."

The meals are simple but tasty--and nutritionally well crafted. Lunch is a Tupperware container of whole-grain salad--tabouli, a whole wheat pasta toss, or brown rice and veggies--that we tuck into our Camelbaks and eat on the beach. When we return to the lodge, there's a different blend of freshly squeezed fruit juice each day--pineapple and mango, papaya and orange, melon and apple. Dinner starts with a salad or soup followed by a modest-size entrée--my favorites are spinach gnocchi and a broccoli crepe. When I glance hopefully toward the kitchen, Adriana explains that there's no dessert, not even fruit.

On day two, the diet has pushed me deep into calorie debt. Headachy and cranky from the abstemious meals, I'm struggling to keep my feet moving on the hikes. Determined to stick with the plan, I try to picture myself sliding into my skinny jeans. By the next day, my body has reconciled itself to the new food regime, and I experience the clear, light feeling that a lean diet can produce. With youth on their side, Kjerstin and Jean have escaped the hungries and are thriving on the small meals.

As the days blur into a happy haze of brisk land and water workouts, a few activities stand out. One day, we take a motorboat to the island's main town, Abraão, where a long stretch of beach is fronted by a cheerful line of T-shirt and sarong vendors, snorkel- and scuba-rental shops, and open-air cafés. I find it difficult, though, to get past the scoop-your-own-cone ice cream place, passing it with a sigh. We hike to a big sweep of beach overhung with sea grape trees. This is a soccer-loving land, and an ad hoc match immediately strikes up: Brazil versus the rest of the world. Jean, a strong swimmer, dives into the lively waves, while Kjerstin and I stretch out on the sand and watch the guys strut their stuff, bouncing the ball off their heads and knees.

On other hikes, we encounter more somber aspects of Ilha Grande's history, visiting the ruins of a quarantine facility turned penitentiary, one of the island's two prisons. Their presence preserved the pristine state of Ilha Grande's beaches by keeping tourism at bay: It didn't develop here until a decade ago, when the second prison closed. (Much of the island's extensive rain forest is now protected parkland.) Another day, we hike past a rock-lined pool where African slaves who once worked on sugar and coffee plantations here were taken to bathe. An iron ring to which they were shackled protrudes from a rock. "The island has a tragic past," Steve says. "We're here to correct the karma."

One evening after dinner, a team of dancers perform capoeira, a Brazilian martial art developed by African slaves five centuries ago and set to traditional music played on a berimbau, a single-string instrument that looks like an archer's bow. After pairs of well-muscled men execute graceful fight-like moves similar to those of American break dancing, they invite us onto the dance floor. I stumble over my two left feet, but Jean catches the rhythm instantly, swinging her leg over her partner's head as he crouches low, then squatting as he "attacks" her.

For our final day, we opt for a different sort of physical challenge, tackling Pico do Papagaio ("parrot's peak"), a big green mountain that rises behind Abraão and is capped by a rocky massif that resembles a parrot's head. Many guests pass on the steep three-hour hike to the summit and head for the beach instead. But we want to end our week with a bang, and as soon as we set out, I'm glad. Unlike the broad beaten-earth paths we've walked here, this one has a true rain-forest feel, with thickets of bamboo and dripping foliage tickling us on both sides. We hear the distant calls of howler monkeys, and we watch leaf-cutter ants march by toting impossibly bulky loads, like so many floats in the Rose Bowl parade. While we struggle for purchase on the steep, muddy grade, Martin glides along in flip-flops. For the first time this week, the weather fails to cooperate: The summit is shrouded in clouds, and we miss the nearly 100-mile view. "Hey, it's a reason to come back," Kjerstin remarks, and truly, nobody is disappointed. The effort has been its own reward.

After marching 3,200 feet up and 3,200 feet down, my quads are pleading for a good massage. I'm in luck: The Island Experience's rubdowns are first-rate. This last night, I draw Sondra, one of two short, stocky middle-aged women from town whom I refer to as the tough-love twins. They both give a no-nonsense pummeling that has my muscles simultaneously screaming for mercy and begging for more. Earlier in the week, I have a superb Thai massage from Gabriela, a Mexican therapist who now lives in Rio and regularly travels to Ilha Grande to work at the Island Experience. The yoga classes win the program another gold star. Bruna, a curvy Brazilian with a magnificent full-back tattoo of Saraswati, the Hindu goddess of wisdom, leads the morning class. Flow is the name of her game, and we move smoothly from asana to asana, following her husky Portuguese accent: "Inhale. Fill your bah-lee with air." In the afternoon, Bruna's significant other, Daniel, whippet-thin with a two-tone mane of dreadlocks, tailors his class to soothe the muscles we've worked that day. One afternoon, when I'm his only customer, he shows me some stretches to address the limited mobility in my shoulders. By the next day on the trail, he's thought up a few more for me.

This is the beauty of such a small group. We get lots of personal attention, and if each of us were to desire a different activity plan for the day, the staff could handle it. Even with a full house, the resort prides itself on customization and, if necessary, will assign a trail guide for every guest to accommodate individual fitness levels. Over breakfast the last morning, Jean, Kjerstin, and I compare notes. Kjerstin feels recharged and ready to tackle the rigors of life in Africa and fund-raising for her organization, and Jean, too, feels rejuvenated. "I haven't spent a lot of time here formulating a new career plan," she tells me, "but I know the answer is percolating up during these days of eating well, exercising, and escaping my day-to-day." We all feel leaner, fitter, calmer, stronger.

In the end, the magic of the Island Experience is the passion its founders have for the place, and the depth of their knowledge of physiology, nutrition, and exercise. Adriana, Martin, and Steve launched the business not to make piles of money--with so few guests, that's not in the cards--but to create a rewarding life for themselves. As my enthusiasm for their adopted home grows, my stay morphs into much more than a fitness week. Dinner conversations revolve around what Argentines think about Brazilians and vice versa, and our hikes offer a glimpse of rural island life.

It's an easy place to criticize--an unwavering diet without even a dollop of soy ice cream or a tiny square of fruit cobbler, balconies that are too narrow for lounging, and wily mosquitoes that penetrate our netting at night. But that's missing the point. As one former guest put it, "The Island Experience isn't about manicures. It's a place of absolute calm and extraordinary natural beauty. I slept as I haven't slept in years." Little inconveniences are overshadowed by the power of the program and the fellowship of Martin, Steve, Adriana, Bruna, and Daniel--whom I come to think of as the lean team. For seven days, Jean, Kjerstin, and I are life's happy dropouts, totally taken care of, totally out of touch with the world. No TV, no radio, no phone, no Internet. The news blackout is so complete that I arrive at Rio's airport unaware that Hurricane Rita has blown away my flight home. This would normally send cortisol thundering through my veins, but I'm so blissed out that I don't even care. Better still, when I get home and step on the scale, I know it isn't just my mind that's light: I've lost five pounds.

Rates Six-night package, $1,900. The rate includes accommodations, all meals, activities, five massages, and round-trip transfers from Rio International Airport (a 2.5-hour car and boat trip each way). To enter Brazil, U.S. citizens must have a visa, which will run about $100.
Reservations 347-416-6517
Website www.theislandexperience.com

Susan Crandell is the former editor in chief of More magazine. Her book, Thinking About Tomorrow, was published in January.