Delving deeper into the ancient mysteries of the Incas, this installment of "Nova" takes viewers to the famed archaeological ruins of Machu Picchu, a sacred Peruvian site that remains a marvel of modern engineering. For reasons yet unknown, Machu Picchu was abandoned in the late 16th century. But what was its purpose, and what really happened to its original inhabitants? Join archaeologists as they explore untouched areas to find out.