My children began counting caimans -- South America's crocodiles -- as soon as our motorized dugout canoe took off at dawn up Peru's Upper Madre de Dios River. Twelve hours later, as we glided into the dock at dusk, caiman number 18 was gliding out.

In the Manu Biosphere Reserve, caimans and other untethered creatures vastly outnumber Homo sapiens, tourists included. We spotted only two of those during a refueling stop, and they were perceptible only with binoculars.

Our destination: Manu Lodge, a thatched-roof, 10-room structure made of fine Spanish cedar logs beached by floods years ago and polished to a handsome shine. It had taken us three days to get here from Cusco, our base for the first week of a two-week trip to Peru hiking the Incan ruins of Machu Picchu and surrounding Sacred Valley.

The trek included a jarring 10-hour ride in a truck along a dirt road so narrow it required several three-point turns where waterfalls had washed away the road, and a two-day stay at the lovely Manu Cloud Forest Lodge, at the southern tip of the reserve next to a rushing river and 400-foot-high waterfall.

Now, we stepped out of the canoe onto slippery palm fronds laid atop the deep mud. In vanishing daylight, we hiked the last half-mile to the lodge. Gigantic hanging vines and spider webs, and the thickness and dampness of everything, made us think twice about our big vacation.

But the idea of escaping cell phones, BlackBerrys, laptops and the news, all for only an hour's time difference from the East Coast, had been too alluring to pass up. Besides, in the era of post-Sept. 11 terrorism, South America is an al Qaeda-free zone, although narco-traffickers, various guerrilla groups and ordinary crime are as prevalent as ever. Peru's own insurgents, the Maoist Shining Path, were all but vanquished more than a decade ago. Happily for us, the tourist industry hadn't caught up, and our days in Peru were pleasantly uncrowded.

The first pitch-black night in the rain forest, though, required some adjustments. Red howler monkeys roared like the afterburners of F-16s. The pauraque, a cousin of the whippoorwill, squawked to a beat. Cicadas competed aggressively for a place on the sound waves crashing through the netted canopy that protected each bed, and each sleeper, from the Wild Things.

Our kids, then 8 and 13, were restless and worried.

"What if something happens?" asked the 8-year-old.

"Nothing will happen," I answered, mustering the most relaxed voice I could, considering it had just dawned on me that a rescue plane would take eight hours to evacuate anyone, and then only if the shortwave radios worked as advertised.

"But what if it does?" she persisted.

It was a logical question -- but, by the second night, no longer a concern. And by the third night, no one was even complaining about having to stumble alone out the door, through the mudroom, down the steps and along the log path, flashlight in hand, to find the ecologically friendly bathrooms crawling with not-so-tiny night life.

In the bright blue morning, the jungle of southeastern Peru -- the most isolated, inaccessible and magically beautiful place I have visited in a decade of reporting around the world -- beckoned with adventure.

The Manu Biosphere Reserve is a sort of buffer zone for the much larger Manu National Park, which is about as big as Switzerland but is off-limits to all but authorized researchers. Located along the eastern slopes of the Andes and sliced by a tributary of the Amazon River, Manu is one of the world's largest biosphere reserves, a U.N. designation for land that includes one or more protected areas managed by the government to promote both conservation and the sustainable use of natural resources.

As our tour operator's pre-departure guide pointed out, there is actually little "jungle" in the reserve. The vast lowlands of the Amazon Basin are correctly termed "rain forest," but they call it a jungle anyway. There are no herds of antelope sprinting by the Range Rover, either. A rain forest quest is one of tracking, listening, patience.

It boasts 1,000 bird species, 1,300 butterfly species and five different landscapes, each with its own climate, geography, flora and fauna.

Only 800 people visit Manu each year, according to the records at the Manu Wildlife Center, the park's visitors center. There are only three lodges and one tent camp in the buffer zone. All are privately owned concessions that operate within government rules on trash and human waste disposal. Tourists must come in with dedicated guides and are grouped with other small parties that have also hired an authorized guide. Ours was 29-year-old Edward Montalvo, and he was the key to our happiness. Edward's parents, he laughed, thought they were naming him "after an American president, Edward Kennedy."

Well, close.

With a master's degree in biology and a special interest in ethnobotany (the study of how plants are used in a particular culture), Edward could spot a flock of macaws two miles away and a rare bug or leaf inches beyond our footsteps. He heard birds long before he found them with his high-powered binoculars and tripod, which he carried on his back. He helped us find not just a couple of monkeys but enormous troops of monkeys swinging through the second layer of the triple-canopy rain forest.

If you're the kind of vacationer who likes to get up early and keep moving, but your husband and teenage son would rather crack the lodge door at 10, then Edward is your man. With a daily itinerary that began with breakfast at 5 a.m., Edward took the nagging out of the trip. No one wanted to disappoint him. And he didn't want us to miss even one sunrise, or one spider, or one moment of perfectly still bird-watching atop a 30-foot-high lookout.

"I love the nature, and the nature loves me," Edward told us over dinner, as we pried out his life story. A soft-spoken man with the broadest of smiles, Edward preferred, he said, to live mostly alone, in the jungle, than anywhere else in the world. He brought us up into a treehouse, constructed 100 feet up a graceful ceiba tree, and served us a pancake breakfast as the deep orange sun came up and the parrots flew by. Then he coached us, one by one, into actually letting go of the platform and dangling down with only a rope harness. Squeals of delight came from everyone -- age 8 to 57 -- on their acrobatic descent.

Even more, Edward let us see the rain forest through his eyes. He found three-dimensional spider webs, see-through butterflies, the pseudo-suicidal fern (which goes limp when touched, to protect itself) and the amazing vine-tree that "walks" as it devours its host tree. With infectious wonder, he would stop suddenly and point to a hollowed-out tree trunk surrounded by the new tree. There, crawling up the moss, would be a rare primitive spider, with fangs that flex up and down, not to be confused with modern spiders that bite horizontally.

With his bird-watching help, we spotted the hoatzin, a unique prehistoric species; giant hummingbirds; the elusive, crimson-colored cock-of-the-rock; and two species of trogons. On the two occasions we climbed above the rain forest canopy, we discovered not only an elegant, gauzy sunrise but four species of macaws and their bright green parakeet cousins. Not quite beyond the range of his binoculars, we spied a huge crimson-crested woodpecker.

The only thing Edward ever missed during our six-day trip was the formation of miniature army ants that my daughter and husband stepped on, only to be dancing and stripping a split-second later. The one disappointing afternoon he gave us was a windless, 100-degree catamaran ride across an oxbow lake to look for endangered giant river otters, which were, apparently, too hot themselves to venture beyond the shore.

Even then, we had the lodge, well-stocked with cold beer, wine and soft drinks, and our lovely bare-bones room, complete with mosquito netting over each of the single beds, a bucket if the trip to the outdoor bathroom seemed too far, a hook for wet clothes and fans for the middle of the day when it was too hot to move.

Papaya, pancakes and hot chocolate were staples for breakfast. A box lunch of rice-and-something was offered to eat out on the trail, and dinners were a just-below-gourmet variety of beef, chicken, fish and fresh vegetables, topped off with entirely satiating desserts.

But best of all, we had our fellow travelers, two couples who had been grouped with us.

Our lesson in biodiversity was not limited to the jungle.

Cindy and Susan were fiftysomething housemates from Northern California. They had rented mountain bikes in Cusco (an option from the tour company), gotten off 10 miles uphill from the first lodge and raced the bus in. Susan, a nurse practitioner with a personal pharmacy in her knapsack, had nursed my son back to health with her uproarious laughter and just the right medication when he contracted what he gamely named "El Flu de Peru."

(At that moment, I felt like a total flake of a parent, having brought only a bagful of expired over-the-counter pills for hay fever and the like. Same with the forgotten rain jackets. Thank goodness for the $1 plastic ponchos we had bought in Machu Picchu the week before.)

When Betty and Pierce arrived on a second bus, we all held our breath. She wore diamond rings as loud as her Texas accent. (They raise cattle on a 60,000-acre ranch in west Texas.) He had been appointed by then-Gov. George W. Bush to the Texas prison board. Cindy and Susan were die-hard liberals.

But we all bonded immediately. When politics came up on the fourth night, everyone explicitly and politely searched for the middle ground to every issue.

The four of them traveled together with their guide by day, and otherwise helped our kids keep count of the 15 capybaras, 57 caimans and 73 turtles they tracked along the riverbank.

We saw not one other tourist during the entire five-day stay in the jungle. And not a single scrap of trash, either.

When we went looking for black caimans one moonless night, I spent most of the time with my head rested against the railing of the quiet catamaran, listening to the water brush by and taking in an entire galaxy of stars, the likes of which I have never seen, and can still see now.

To be honest, the trip out of the jungle became a little too harrowing when the outboard motor on our dugout canoe faltered and 12 hours turned into 15, the last three in the dark and without the life vests promised in the brochure. The harbor in the tiny outpost called Laberinto, near Puerto Maldonado, where we finally docked at 10 p.m., reeked of marijuana.

When the kids returned home to Washington, they declared they would never go into the jungle again. I worried about blowback.

But after six months, they began begging for another adventure vacation. Thinking tame, I suggested Costa Rica. "Costa Rica!" the 8-year-old frowned. "I want to go somewhere really different. How about Cambodia?"

"Yeah!" added my 13-year-old. "Then on to China."

Dana Priest is a reporter on The Post's national staff.

The Pinquen River in Peru meanders through the isolated, barely touristed

Manu Biosphere Reserve, which contains some of the world's most diverse

flora and fauna (including the caiman, right). At top right, visitors can

explore the rain forest by propelling from treetops. The Manu Cloud Forest Lodge, on the southern tip of the Manu Biosphere Reserve, is surrounded by the rain forest and its inhabitants, including red howler monkeys.The Manu Biosphere Reserve is home to 1,000 bird species and 1,300 butterfly species. A caiman, the South American crocodile that in some places outnumbers humans, rests on a river bank.