Carlos brought mate de coca and hot water for washing to our tent at six the next morning. It had rained during the night. But here, at ten thousand feet above sea level, we had a clear light for the big day at Choquequirao, the City of Gold. We left Felicitas, Carlos, and the mules to rest for the day. The path was level. And around the next bend, finally, Choquequirao.

We were still two hours away, but finally we had a sense of what we had hiked down and up a canyon to see. A puzzle, a mystery. Across the ravine and a thousand feet below us, a series of terraces, impossibly steep, had been excavated. Farther up the hill was another set of terraces, partially cleared but still with large clumps of trees. Far above the terraces, directly across from us, was the perfect helipad of the ushnu, "the sacred meeting place of Choquequirao," Ana said. And above that, joined by a neatly mown plaza on the ridge, was more of the site. At this distance, Choquequirao was a giant Sudoku with only a handful of numbers penciled in. In comparison, Machu Picchu is a fully filled color-by-numbers.

"People have known about Choquequi­rao for centuries," Ana told me. "There was a French explorer, the Count de Sartiges, in the 1800s. But before him there were Spaniards." And after. Some say the city was built during the reign of Pachacutec in the mid-1400s and became the last refuge of the Incas under the final ruler, Manco Inca, a hundred years later. Others say that pieces of pottery found at Choquequi­rao show that it was inhabited hundreds of years earlier. Each successive visit by anthropologists and archaeologists brings a new theory. And yet Choquequirao gave off a whiff of inscrutability as we came around the bend in the ravine.

"When I was a little girl," Isabel had told me down by the river, "I lived at Marampata and looked after the cows. But my uncles told me that Choquequirao was full of ghosts. 'Never go there,' they warned. Even when a cow wandered off into the ruins, we left her for the ghosts."

There was something ethereal about Cho­quequirao as we walked out of the trees and onto the paved terrace leading to the deserted city. City may be too grand a word for what has been uncovered so far. Choquequirao is compact in its emptiness. There are a couple of town squares and a handful of Incan stone buildings like the ones at Machu Picchu, with tapered doorways and intricate niches and hooks for hanging lamps or securing ropes for the roof thatching.

Ana pointed out a set of protruding beams at the level of the second floor. "Balconies," she said. "The Incas didn't know about balconies before the Spanish came. There are no balconies in the houses of Machu Picchu, only here." It's a small marvel, a modest discovery.

The latest find is one that hasn't yet made it into the books or blogs on Choquequirao. Four years ago, terraces were discovered on the far side of the mountain, the side away from our approach. On the walls of these terraces, in crude mosaics of white stone, are the figures of twenty-three llamas, some adult, some baby llamitas. Former first lady Eliane Karp has grandly taken some of the credit for this discovery. But as with everything else at Choquequirao, it's hard to know what to make of the llamas.