El Castillo, Chichen Itza, c. 1000 AD — the 30-meter pyramid encodes the Maya solar calendar in stone, with 365 steps total across its four staircases. At each equinox, afternoon shadows create the illusion of a feathered serpent descending the northern staircase to meet the carved head at its base.Gary Todd from Xinzheng, China, CC0, via Wikimedia Commons
