National Geographic Society

The Pyramid of the Sun (top) is the largest structure in the ancient city of Teotihuacan, Mexico, and one of the largest buildings of its kind on the Western Hemisphere. It stands 216 feet (66 meters) tall and measures 720 feet (220 meters) in width at its base.

Originally built as a smaller structure around A.D. 200, the pyramid was added to several times before it reached its current dimensions. It stands over a network of caves and tunnels, which archaeologists think were spiritually significant to the mysterious builders of Teotihuacan.