IT was our first day in this remote Guatemalan outpost: We had no way of gauging understatement when Mr. Campbell told us it would be "a little wet" to take our cameras on the three-mile boat trip up the Caribbean coast to see the Seven Altars waterfall.So when he killed the motor about 100 yards off shore of the waterfall and told our party of six Americans to swim for it, we snorted indignantly and refused. It took the pounding surf almost upending the boat to convince us to jump, or be tossed. After a longing glance at the life vests tied hopelessly in knotted bundles, we each leapt into the warm Caribbean fully clothed and paddled madly for the distant forest. This is not the Caribbean of cruise ships, package deals, and tourist resorts. We had embarked from the Yucatan a week earlier on a sailing tour of the backwaters of the Central American Caribbean. The object of the trip was a more uncooked and adventurous kind of travel. And on this 45-quetzal ($20) side-trip from our 38-foot, sloop anchored at Livingston, we were getting it on the cheap. Straggling ashore, the urge to whine turned to helpless laughter as tall tales to be told back home began to take shape. The trek to the waterfall was a turning point in our trip. It helped to crack our rigid sensibilities and expectations. Instead, we lounged in the cascading pools of the waterfall, as cool as the surf was warm, and watched the sea from beneath a rainforest canopy. Later, asked why he didn't warn us about the swim, Mr. Campbell answered in his creole English lilt: "You didn't ask." Perhaps that is the point of adventure travel: Not knowing what to expect - or, indeed, what to ask. An open mind is the best ticket to get beyond the gaudy tourist paths of the Caribbean. Ours was a two-week sail from Isla Mujeres, Mexico to Belize and up the Rio Dulce, its mouth accessible only by boat or small plane. The sailing itself was a day and night marathon. A delight for the old salts aboard, for the uninitiated it was akin to camping on a rollercoaster - torn between queasy disorientation and the exquisite beauty of sea and sky. The journey south from Mexico is like successive steps back in time and development. Surroundings get simpler; the environment, not entertainment, becomes the attraction. Though the Isla Mujeres-Cancun area, as well as Cozumel, are friendly and clean, they largely reflect American tastes: hotels-cum-cathedrals-of-tourism and endless cantinas with names like Mama de Tarzan. After simmering in the tropical swelter for nearly a day at a rickety Belize City dock waiting for customs agents to clear us, we had just 24-hours to explore beyond the tropical decay of the city. We drove a rented jeep ($100 a day) to the Mayan ruins of Altun Ha 30 miles north of town. There was little to suggest that we were headed for anything of great import - no road signs, no billboards. So when we burst upon a palm-ringed opening, Altun Ha made an awesome spectacle. While not the best-preserved or even the most dramatic of ruins, Altun Ha offered an intimate solitude we were all alone in the dead quiet of the breezy plazas and looming pyramids, left to ponder the 2,000-year-old symmetry and grandeur amid the dense forest. Livingston is a colorful jumble of cultures: the black Garifunas are lively, creole-English-speaking descendants of escaped St. Vincent Island slaves, and Spanish-speaking Mayan Indian descendants quietly come and go in sleek, dug-out cayucos. We ate at Livingston's Malecon restaurant, following a tip from a tour-book. We overlooked the bare-bulbed lighting, uncomfortable chairs and the wandering mutt that sniffed his way through the dining room to the kitchen. We were rewarded with huge and deliciously garlic-dosed servings of fresh lobster, grilled bass, shrimp and even a lone steak. The tab for six? Less than $25. The next day as we began to motor our way up the misty jungle gorge of the Rio Dulce River, we saw where our fish had come from. Indians, from tiny 5-year-olds to adults, stand gracefully on narrow canoes, twirl 30-foot casting nets over their heads, and let fly. These fishermen live and work along an undeveloped 18-mile stretch of river accessible only by boat. Cascading vines and thick tropical vegetation cover the steep canyon, and the misty bends and quiet inlets make it easy to imagine the 17th-century pirates who plied these waters. Anchoring for the day about 10 miles up the river, we were visited by some fishermen. For less than a dollar, we bought that night's dinner, which was cooked over a small barbecue attached to our boat railing. A Kekchi Indian named Jorge, traveling on his motorized cayuco with his wife and infant son, sold us the vegetables. He also took us to the nearby Rio Tatin, a small tributary of the Rio Dulce where we got a glimpse his family's cluster of dirt-floor, thatched houses a couple of steps from the river's edge. We also met the region's visionary who has begun building a small eco-tourism inn along the Rio Tatin. A French investor in Guatemala City during the week, John Heaton met us in shorts and knee-high waders caked in the stubbornly thick red forest mud. Leaving his blueprints draped over a table, he walked us across the rainforest hillside where his vision meets regular resistance from land slides. The shells of several thatched structures gave us the first real chance to learn how the palm fronds are tied together in what he testified is an absolute water-tight web. The grooves of fronds, he explains, are all placed facing upward and are layered so that water runs through the grooves and off the roof. The only problem, he says, is that thatched roofs are popular nesting spots for scorpions. The next day, we had wind enough to sail on into Lago Izabal. All the way along, we saw signs of deforestation dotting the green hillsides: by day scorched earth and gray smoke; by night the red glow of fires. On our return trip downriver, close to the Rio Tatin, we looked for a sulfur hotsprings following vague directions from local boatmen like "just across from that hut" or "just around that bend." A half-hour after moving up and down river, we finally got warm. Beneath a canyon wall of hanging vines along the riverbank, hot water surges quietly from inconspicuous limestone rocks, smelling of sulfur. Floating in the warmth, we were happy just to be there.