When the Spanish Conquistadors swept through Peru in the sixteenth century, they were searching for great golden treasure. In 1572 they stormed the Inca stronghold of Vilcabamba, only to find the city deserted, burned, and already stripped of its wealth. A legend says that the Incas had retreated deep into the jungle, where they built another magnificent city in an inaccessible quarter of the cloud forest. And for more than four centuries...