As Karas' prior livelihood uniquely qualifies him for his present vocation, so does that of Nathaniel Mas. A Maya himself, he worked on the excavation and renovation of Nim Li Punit, the ruin situated a couple hundred yards uphill from Indian Creek Lodge. "If it was the old times," says Karas, "Nathaniel would be the head mason for the Maya ruler." So Karas put him to work building stone walls for the lodge and showing guests around the site. He does so with an obvious sense of pride — we discovered these artifacts of our culture, and I myself discovered this tomb.

Built in the 8th century, Nim Li Punit was a royal observatory. The on-site museum's claim to fame is the second-largest Maya stela, whose chiseled legend Mas decodes for us. As he guides us around the grounds interpreting the altars, tombs and ball court, he also stops at all the major plants to demonstrate the bushcraft that goes into living off the local environment. As a bonus, he takes us to his family compound between the ruin and the lodge to show the results. His home is made of tree trunks and planks bound by vines and topped with thatch, as Maya homes have been for eons. Hammocks are slung across barely furnished rooms. I take the opportunity to ask Mas' 41-year-old mother to compare the time when the acreage across the road was farmed and logged with the eco-sensitive era brought on by development of the lodge. I'm surprised to learn there's no difference as far as she's concerned.

But to Nathaniel and another BLE guide, Thomas Pop, who takes us on a cave trip the following day, things are much better now. The lodge employs 125 people, many more than the farm did — all the men from neighboring villages can now find work without having to leave their families and can afford to send their children to school, which most of their parents could not do. And the work is more agreeable, too. Pop, 39, worked the banana fields for nine years and spent four years in the army. "I guarantee this is a better job," he says. "In the army you have to sit in the water for 12 hours at a time, making river crossings. Now I'm driving around with a cooler in the back."

On the way to Tiger Cave, Pop stops in a Maya village to pick up Pablo Ack, a local guide who reports that he commonly sees fresh jaguar tracks hereabouts. After a short hike through a broadleaf forest, we come to a gash in the face of a karst wall and duck in. The entrance quickly opens into a vast cathedral-like space, dimly limned by a slash of sunlight piercing the ceiling eight stories overhead. Ack shines his flashlight on the cave floor, playing over pottery shards estimated to be 500 to 600 years old. He explains that until the cave became a tourist attraction in recent years, Maya elders performed rituals here. We come to a perfectly sculpted altar that looks handcrafted, but it's a natural formation made of sparkly limestone. This is where the elders would sacrifice mice to the corn gods so the rodents would stop devouring their crops; such practices are still carried on today, Ack says, at a more discreet locale.

We delve deeper into the cave, and at one point Ack suggests we stand still and douse our lights in order to experience the powerful combination of pitch-blackness and silence broken only by the cheeping of bats overhead. We clamber onward. At some points the cave is silty and slick like a riverbed; at others the path becomes a rocky tunnel that requires climbing. I gradually feel myself regressing to a childlike apprehension of the cave as font of mystery and myth, a role it has always played for the Maya as part of the multi-layered Underworld. As the journey becomes more and more strenuous, and we all become covered with a heady patina of sweat, mud and batshit, the divide between guide and guest dissolves; we're all in this together, and it's officially an adventure. It's a great feeling, as is the post-spelunking picnic lunch and swim in a pool formed by the fresh headwaters of a river as they spill from the mountain.

Golden Stream is not only the main artery of the ecosystem Karas is working so hard to preserve, it's also the only way to reach his Jungle Camp. Which is why I'm paddling a kayak down a jungle waterway overgrown by trees with patchy camouflage bark. We've pushed off in mid-afternoon because tapir are often spotted in the stream as the day wears on. I'm eager to see Belize's national animal because, well, they're funny-looking: up to 875 pounds, thick of body and short-legged, with trunk-like snouts. But all I can spot are the mudslide tracks where they enter and exit the stream. I perk up when I hear some snorting and snuffling, and find myself locked in eye contact with a curious-but-wary wild pig that quickly turns and scoots off into the bush. The stream is draped with vines covered in little white bouquets that create sweet pockets of fragrance, like honeysuckle but stronger. Those spots are an antidote to the other vines that give off a smell more evocative of a 7th Avenue subway staircase in late July. That's biodiversity for you. Three hours of steady stroking brings us to the camp, where it looks as though Tarzan has been working overtime. There's a thatched-roof main building connected by a catwalk to a string of six huts stacked on steel stilts 20 feet above the stream, as a precaution against floods. ("I took the local style and super-sized it," says Karas of his design and construction modus.) Once again, we've got the place to ourselves, and the hosts are clearly happy to have us.

Entering my room, I'm pleased to find that the native building materials are exposed, the shower works fine and there's furniture on the porch overlooking the water and jungle canopy. And despite the remoteness of the camp, the standard of cuisine is maintained: Earlier today, at Indian Creek, lunch was a lobster quesadilla; tonight's dinner at Jungle Camp is thyme-marinated filet mignon, with yampi gratinado and demi-glace provençal. With this combination of deep wilderness, high comfort and total exclusivity, Karas has achieved his Central American safari ideal.

In the morning I set out with the kayak guide Antonio Shol for another session of tapir spotting. "If you hear a cuckoo on the right-hand side, that's good luck," Antonio says, and sure enough, we soon hear one on the right. As we paddle back upstream, Antonio identifies the various fruiting trees and the birds that favor them. He points to a snag above the canopy where some toucans, with their comically outsized brilliant yellow-orange beaks, are resting. A pale-billed woodpecker with a crimson head hammers on a dead trunk; a hummingbird flits around a stream-side vine, its wings whirring like a tiny electric fan. An Amazon kingfisher skims the surface ahead of our boats, as if reconnoitering for tapir on our behalf, albeit unsuccessfully. Antonio explains that tapir walk underwater, submerging for minutes at a time. I say hippos do the same, but he's never heard of them. I start trying to describe them, but despair of doing justice to such an outlandish beast. Then Antonio starts talking about kangaroos, which he saw for the first time last night on a DVD movie in camp. He says they're tall and fast, and asks me where they come from and whether they can speak, "the way you and I are speaking now."

No they cannot, I regret to inform him, but I am very glad he asked — his complete ingenuousness is as sweetly refreshing as it is hilarious. Here's a young man who speaks several more languages than I do, knows every bird in the jungle, who sees a kids' movie and thinks kangaroos can talk. The MTV revolution has definitely not been televised in this part of Belize.

Antonio and I spend a good chunk of the afternoon paddling downstream, where the bush thins out to allow a different kind of seeing, clearer and more vivid; individual ceiba trees appear grander, against a bluer sky. It's probably just due to better light, but I feel my perception and appreciation is being sharpened by exposure to the jungle, the remove from civilization's chatter. For a long time we watch a family of four howler monkeys feeding in a big tree; a pair of iguanas sun themselves in another. I paddle in close to study a citroline trogon perched on a branch hanging over the stream; it's exquisite, plump with a yellow breast and brilliant blue-green-violet back and tail. We marvel at the dangling colonies of Montezuma orapendola nests, and the bizarre bowing gesture the bird makes when it calls.

In two days on Golden Stream we encounter no strangers. I'm so completely immersed in this lush, wild environment that occasional airplanes passing overhead momentarily jolt me from the reverie with a reminder that the outside world is not so far away. Still no tapir, but I fully concur with Antonio when he remarks at the end of six-and-a-half hours of paddling, "The cuckoo gave us good luck today."

No trip to Belize would be complete without a snorkeling excursion to the reef, and the lodge provides a skiff to ferry us the nine miles downstream to Port Honduras Marine Reserve. There we are greeted by a curious dolphin and exactly zero other boats. We stop to see two-acre Moho Cay, where Karas will soon begin building a lodge, another link in the chain. From there it's another 30 minutes out to the vast barrier reef that stretches all the way up the Yucatán. As soon as I plunge into the water, I find myself hovering over a spotted eagle ray; the moment I lose it, a southern stingray enters my view.

A few days ago I was caving in the Maya Underworld, yesterday paddling through tapir and toucan territory, and today I'm catching rays on one of the world's great reefs. What a place. No wonder Ken Karas fell in love with it and wants people to see it at its natural best.

Contact Belize Lodge Expeditions: 888-292-2462, 011-501-223-6324; www.belizelodge.com. Closed August and September.