La Flânerie is on the Adour River, in a delightful rural backwater so untouristed that few of its towns can be found in the guidebooks. Rich in history, it is an agricultural region in Gers, the only French département that has experienced a net population loss since the mid-nineteenth century. Charles de Batz-Castelmore, a knight in the service of King Louis XIV and Alexandre Dumas's model for the musketeer d'Artagnan, lived nearby, and his home is now a small museum.

Upon our arrival, Nicole introduced us to Cabeilh. She was a statuesque Pyrenean donkey, a breed distinguished by its white muzzle and potbelly, black or brown body, and long ears. She was one of about a hundred that the Guyots raise on their farm in the foothills of the Hautes-Pyrénées.

Nicole advised us to hike with Cabeilh for four days in the valleys before tackling the mountains. We learned how to care for Cabeilh, how to brush her down each morning and evening and to pick the stones out of her hooves. It was mid-August, and we walked 56 miles along footpaths and dirt roads in 90-degree heat. The sun beat down upon us and on the endless fields of grapes, soybeans, haricots verts, and feed corn we traversed. For fitness-obsessed New Yorkers like us, this was a wonderful workout even though it involved no machines or music.

For much of our journey, we followed the red and white markers of the Grandes Randonnées, or GR, a network of foot trails that crisscross the French countryside. Topoguides—detailed maps of the GR—show every path, campsite, and asphalt road in the area. Property owners are required to keep the paths open to hikers.

At other times we followed the orange markers on trees and fence posts, which indicated one of the medieval routes across the Pyrenees to Santiago de Compostela, in Spain. Beginning in the tenth century and throughout the Middle Ages, millions of pilgrims, no doubt accompanied by their faithful but agnostic donkeys, crossed these mountains to visit the tomb of Saint James, the first apostle to be martyred. Many devout Christians still make this trip on foot. One day, we stopped to picnic beside a twelfth-century church. A local woman approached and offered to put us up for the night. In a ritual as old as the pilgrimage, she explained that she was not listed in the guidebooks, "because the government would come after me with its inspectors and taxes, but truly my prices are the best in the area." We declined.

Donkeys are the perfect hiking companions, much better than horses, because their natural walking gait is the same three miles per hour as a person's. Each day Cabeilh carried two gallons of water for us. She herself, however, never stopped to take a drink. Like camels, donkeys can store water in their bodies for long periods of time. Each evening, we would lead Cabeilh to a trough or spring, and she would dunk the white part of her nose into it and noisily imbibe more than a gallon of water. Other than that, like W. C. Fields, she never touched a drop.