Sacsayhuamán is an impressive Inca fortress located on a hill overlooking Cusco. Built in the 15th century, it features massive stone walls with some individual stones weighing over 100 tons. This UNESCO site represents the pinnacle of Inca engineering, with stones fitted together without mortar in astonishing precision. The site hosts the annual Inti Raymi festival in June. The zigzag walls stretch over 400 meters and offer spectacular views of Cusco below.