High in the Peruvian Andes, the ruins of Machu Picchu rest amid knife-edged ridges and vertical slopes draped in emerald jungle. Hidden from Western explorers until 1911, when a Quechua guide led Yale historian Hiram Bingham to the site, the marvelous Inca city was mesmerizing, even in its dereliction. Built on a granite mountaintop close to the sun, its intricate architecture reveals the ingenuity of its 15th-century designers. Massive blocks of stone were cut to fit together so precisely that no mortar was necessary. The site also reflects the Incas' extraordinary knowledge of astronomy, with many elements aligning with heavenly events such as the solstice sunrise. Far below the ruins, the Urubamba River rushes through a green gorge into the Sacred Valley. Our journey into the mysteries of Inca civilization also includes Cusco, once the gold-laden capital of the empire, as well as modern-day cultural encounters with traditional Andean people who live in harmony with nature.