And then we turned the corner at the town of Capuliyoc and saw what lay ahead. "There." Ana pointed to a bump on a mountain in the distance. "That's Choquequirao." With the sun directly above, we could just make out what seemed to be a handful of man-made structures in the distant trees. Not quite close enough to touch but almost. "And that," she pointed down, "is the Apurímac." We took her word that the twisting white thread below was a river. Far below. One mile below. This was the canyon of the Apurímac, the true headwaters of the Amazon, twice as deep as the Grand Canyon. "And that is our path." A snaky thing. A steep snaky thing, so steep it disappeared at times. And then, across the river, another steep snaky thing. Down one, up the other.

"Daddy . . ." Rebecca began, in a voice I hadn't heard since her eighth birthday.

"I didn't know," I stammered. Bingham's heavily laden mules plunged through my guilt.

In the first hour we discovered at least four ways to get downhill, three of them involving our feet. In the second hour we found that, as narrow and steep as the path was, Carlos and Felicitas and our heavily laden mules were still able to trot along without slipping over the edge. In the third hour, I began to wonder how much this path resembled the one Hiram Bingham had trod a hundred years before. It sliced mercilessly through fields of bloodred wild grass. It slalomed around iron-rich rock slides that looked as if they had happened only moments before. It sought shelter from the unmediated altiplano sun beneath white-blossomed cotton trees laden with vines and orchids. And in the fourth hour, we realized just how appreciative your right quad and your left big toe and your calf muscles can be when you reach the campsite and give them a rest.

Felicitas and Carlos and the mules had navigated the seven miles to the site, Chi­quis­ca, in half the time it took us. The upper site was already packed with the tents of a dozen people, mostly French couples, their bare calves painted with bug bites. Twenty-year-old Uriel connected a pipe to the spring, and we bathed in fresh glacial water using a pockmarked plastic Gatorade bottle for a showerhead. We drank tea and ate popped corn of the giant Peruvian variety in the last heat of the afternoon, as a pair of Andean condors circled three thousand feet above us.

The stars replaced the sun by seven o'clock—first Scorpio, with its two piercing eyes, and, after dinner, the sideways kite of the Southern Cross, rising above us on the south side of the valley. I fell asleep to the sound of the mules rolling in the cool of the dust above camp.

The next morning, we let gravity and alti­plano french toast drag us down the final hill of the canyon to Playa Rosalina, by the banks of the Apurímac. One mile lower than the main village of Cachora, we were in the heart of a tropical climate. Agave and saguaro cactus lined the path parallel to the river. May is the first month of the dry season, and the roar of the river, twenty feet below its high-water mark, was more pussycat than lion. Before the bridge, fruit trees signaled a spring. And within that grove, improbably, was a series of sturdy buildings that resembled an Andean Motel 6.