The Inca were avid stargazers and astronomers; they identified and named not only “light” constellations but dark ones as well—that is, ones formed from the dark portions of the Milky Way. They also laid out some of Cusco's central streets to align with certain stars at various times of the year. At the Cusco Planetarium, you'll learn more about their methods, and their view of the world. Stop in before heading to Machu Picchu so you can put what you learn to test at that sacred site. Reservations required.