“THE LITTLE PERUVIAN MARE stepped gingerly in the bedded tracks of burros, got halfway across the steep sand slide, and stopped. All around us, rock walls the color of a raw wound soared in pinnacles and ramparts, sheer and bone-dry. Fifty feet below, the slide ended in air. And sound. The Cotahuasi River, thousands of feet down, sent up a roar like distant wind as it cut its way into the canyon floor. Ahead, the two-foot-wide Inca footpath was a gray thread clinging to a nearly vertical wall.

I looked at the horse’s ears. It seemed the best place to focus. Her head was low, forlorn, like the woodcuts of Quixote’s Rocinante.

“You want me to get off, don’t you?” The ears twitched. “You don’t trust your footing in this scree and you’re as scared of heights as I am, even though you are Peruvian and bred for the mountains.””