South America's entry onto our list is found in Cusco (sometimes spelled Cuzco), Peru, the city that was once the capital of the Inca Empire and was designated a UNESCO World Heritage Site in 1983. Sacsayhuamán is a great example of this ancient empire's engineering feats. Built without mortar, the stones that make up the wall were cut to fit together like a giant upright jigsaw puzzle. The fortifications zigzag through the site, which sits over 12,000 feet above sea level. The traditional Incan festival of Inti Raymi is held here each year during the Southern Hemisphere's Winter Solstice, and many locals use the open spaces between the walls as a kind of public park.