El Castillo (Kukulcán)
Yucatán, Mexico
Maya step pyramid. Height: 30 m. Date: 8th–12th century CE (earlier substructure c. 600–800 CE).
Temple dedicated to Kukulcán (the Feathered Serpent). Famous for the serpent-shaped shadow that appears around the equinoxes; it is not known whether the effect was intentional.