Cradled by jungle-covered mountains at an altitude of 7,970 feet, Machu Picchu is a labyrinth of mysterious gray stones; the surrounding rock spires seem to form a kind of gigantic natural cathedral. The fabled “Lost City of the Incas” was unknown to the outside world until Yale professor Hiram Bingham brought it to global attention in 1911. The Incas built this extraordinary sanctuary in the mid-1400s — its precise function is still in dispute — but abandoned it almost a century later. Untouched by the Spanish conquistadors, Machu Picchu survived intact for centuries, hidden by dense vegetation.