By Camille Cusumano

Belize’s unspoiled Caribbean shores teem with brilliant sea life. With its 180-mile-long barrier reef and 200-isle archipelago, the Central American country was bound to be a haven for pleasure-seekers.

Snorkeling in warm waters and baking on white-sand beaches sounds wonderful for two days. It wouldn’t raise my pulse for eight. Beyond its seacoast, lagoons, and mangrove swamp lies Belize’s broadleaf rainforest. Twisting paths are overgrown with vines, lianas, and strangler figs. Black orchids and bromeliads proliferate amid mahogany trees and cohune palms. Thousand-foot falls and smoky rivers score the jungled face of mountains. The air waxes with the primordial calls of birds, insects, and howler monkeys, and throughout the forest, dark caves and Mayan ruins wait to be explored.

Put it all together with mountain biking and hiking, and my heart’s approaching its optimum rate. I’m not alone this April in choosing Belize to satisfy a tall order. Fifteen fellow travelers want to burn muscle, observe nature, and absorb culture on this amphibious tour, led by Backroads (of Berkeley). After six days exploring the wondrous rainforest on bikes and by foot, we’ll have our two days of liquid vacation on Ambergris, the largest of Belize’s offshore islets.

There’s not even a token couch hugger on this trip, which makes for one restless group the first day when our mountain bikes have not yet arrived. Our guides devise an appealing alternative in the Yucatecan Mayan village of San Antonio in Belize’s Cayo District.

Belize, an English-speaking country, was British Honduras from 1862 until 1973, but for three millennia it’s been home to Mayans. Our Mayan host provides distraction from itchy feet with a demonstration on carving Mayan gods in black slate, lunch of tamales and corn custard, and folk dance to marimba music. Just when it seems one more minute of "Yellow Bird" on the xylophone might reverse our contentment, our guides immerse us in nature.

In the pools of Rio On, that is, a series of water holes created as the On River flows over tiered granite. It’s our first intimate encounter with the wilderness of a country that scores high for its conservation efforts. Belize aggressively protects its rainforest, wetlands, and wildlife, with many national parks, sanctuaries, and preserves, including one for jaguars.

Our first day sans van is divided between hiking and biking, which brings us to King Vulture Falls. Across an emerald chasm, we train binoculars on the endangered scarlet-headed vultures that nest atop the falls. They pad around like tough guys in black leather and red bandannas. Maybe they’re watching us as we abandon our 21-speed Treks and hike to a vine-choked cascade, where the group’s daredevils leap 30 feet from slickrock into a deep pool.

We have yet to sight the odd-looking tapir, jaguar, ocelot, or jaguarundi said to roam this preserve. But as the day unfolds we get our share of biology lessons—from termites that distend the trunk of a tree and leaf-cutter ants that shear bushes to build "ant condos." We set out an overripe banana and watch a blue morpho butterfly feed on it.

Israel, our Belizean guide, takes the helm, yanking at foliage, branches, and roots. He rubs an iodine-colored powder from one twig and says, "For ringworm in children." He shows us Saint-John’s-wort, the antidepressant, and nine-leaf, used in babies’ pillows. Israel, whose childhood playground was the rainforest, amuses us as he describes a bird’s mating ritual as the Michael Jackson moonwalk. He presses the red rubeosa flower into his mouth and calls himself "hot lips."

It’s a humid 94 degrees and our hardest day of cycling when I find my own identity. We’ve pedaled down the Maya Mountains on rolling dirt roads that are so corrugated, our bones keep rattling even after we stop. We all meet the van with the coveted ice chest in the shanty village of San Igna-cio. You can almost hear cubes sizzle down sweltering flesh.

Gertie, a beauty consultant from New Jersey, and I lean our bikes against the little market and stroll the dirt roads. We give candy to barefoot urchins and locate the cinder-block home of fabled Mayan healer, Don Elijio Panti. As I fasten my helmet and mount my bike, Gertie commands in her German accent, "Come on, we bike together."

She must be delirious, this seamlessly tanned blonde who looks ready for a high-fashion shoot even after a sweaty workout. But as we roll and her jewelry winks at me, I understand. Her eagerness for camaraderie stems from a morbid fear of Belize’s pit viper, the fer-de-lance.

As we strengthen our entourage with Terry from Malibu, I point out that we move more swiftly on bikes than any snake on its belly. Still, every vine or root clawing the dirt road is suspect and causes screams followed by laughter. I divert Gertie’s attention from the harmless striped snake she nearly embosses with her knobby tire.

Having survived all these would-be fer-de-lances, we need a name. "Cranksters" sticks—because we keep on cranking. The "club" provides the synergy we need to brave the heat. Between rounds of aimless laughter, we ford a river, bikes slung over shoulders; seek shade under palm fronds; get lost among orchards and citrus groves; and cross a ranch through cow flops and cattle egrets. We are the only ones to rise from hammocks at Black Rock on the Macal River and straddle our bikes. The rest of the group rides in the van the 8 miles to Chaa Creek.

Chaa Creek, the most magical spot on this trip, rewards our machisma. Its thatch-roof cottages are brightened by kerosene lamps and spread over a hilly clearing in the rainforest with plumeria, birds-of-paradise, and orchids.

We’ve spotted many of Belize’s hundreds of bird species, including parakeets, keel-billed toucans, and an emerald toucanette. But at Chaa Creek, the birds are having a convention. And insects have been invited, crickets on castanets, cicadas on the buzzsaw.

Each night, I imagine these arrhythmic screeches, hums, and groans coming from chanting monks or a John Cage orchestra—not bugs and birds. But one morning, amid the grieving-donkey moan of the game bird chachalaca and mournful call of pygmy owls, Israel points to nearly two dozen species of these racket-raisers. Rainbow-sherbet colors bleed across the lenses of our binoculars as we sight yellow-billed casiques, black-headed trogons, a wedge-tail saber, yellow-tailed saltater, and "that’s-no-banana-that’s-my-beak" toucans.

From Chaa Creek we can hike to undeveloped Mayan ruins, but the restored Xunantunich (Maiden of the Rock) is on our itinerary. Only the Cranksters cycle there. The others ride in the van to the site of this major Mayan ceremonial center. Its pyramid, El Castillo, rises 130 feet above the mounds, temple, and plaza, where thousands of Mayans wove the fabric of one of history’s most sophisticated societies from about A.D. 250 to AD 850. From atop the mossy ruin we sweep in views of the Peten Rainforest and Guatemala.

While the others go tubing on the Mopan River, the Cranksters pedal back to Chaa Creek. I climb a trail to the nature center and am mesmerized watching blue morphos break from cocoons, then hang their wings out to dry like satin parachutes.

Terry and Gertie take their knots and aches next door for massages at Rosita Arvigo’s Ix Chel, a place of healing named for the Mayan goddess of medicine. At Ix Chel, I purchase a few handcrafted "Rainforest Remedies," tinctures of the plants that grow in the rainforest.

Many of us on the tour have been reading Arvigo’s inspiring book, Sastun, My Apprenticeship with a Maya Healer (Harper Collins). An American, Arvigo came to Belize in 1981 to practice natural healing. In San Ignacio, she found Don Elijio Panti, one of the last Mayan curanderas (traditional healers), and asked to apprentice to him. Until Panti’s death at 103 in 1996, Arvigo learned from the bush doctor in his little home/clinic, watching him heal his countryfolk with his hands, prayers, and herbs.

Who would guess that Panti, who drew his pharmacopoeia from among rainforest plants, might leave his mark on modern medicine?

In 1987 Michael Balick from the New York Botanical Garden Institute was in Belize collecting tropical plants to study for use in fighting cancer and AIDS. Balick met and was impressed with Arvigo and Panti. With their help, he eventually shipped thousands of rainforest plants to the National Cancer Institute. Today, the extracts from five plants have advanced to clinical trials for treatment of cancer and AIDS.

Arvigo continues to practice healing the Mayan way. Thousands, inspired by her story, visit Ix Chel. Strolling the Panti Medicine Trail, built in honor of Arvigo’s teacher, I marvel at the ancient tradition that could intuit the healing properties of such scraggly looking plants as hogsplum (for diarrhea), trumpet tree (for high blood pressure), wild grapevine (an antiseptic).

With the jungle simmering, even the Cranksters are done with cycling, but not adventure. We visit Chechem Ha, a Mayan cave site with incense burners, altar, and pottery jars with morsels of corn. It was discovered in 1989, when the landowner’s dog chased a paca into it.

Our last jungle adventure shows how movies indelibly mark us. A handful of us just have to do the "Me Tarzan" swing from this vine. Johnny Weismuller made it look so easy. Not.Getting to that vine was just as tricky. It required a 2-mile scale down 400 feet of limestone cliff, a walk through a waterfall, and an upstream swim in the Macal River.

Once we’ve done our jungle time, we can eagerly watch the rainforest give way to hibiscus, bougainvillea, and the blue Caribbean. We’re one adaptable bunch, donning snorkels and fins to swim with the sharks at Shark Alley and, at Hol Chan Marine Preserve, dangle in awe over sea fans, sponges, parrotfish, triggerfish, and eels. For color, Belize’s brilliant coral and reef fish rival the country’s iridescent birdlife.

Despite being type A travelers, we really enjoy the pace of paradise—and margarita hour at our beachside lodging. One day we really kick back and boat over to Caye Caulker, a smaller islet, to lunch on local snapper. The sand streets are filled with friendly Rastafarians and American expats drawn to the ’60s feel. Shop signs sum it up: "No shoes, no shirt, no problem." Really, I can’t think of a more suitable ambiance in which to return to our resting heart rate.