Chichen Itza

20.6843°N, 88.5678°W.

Pre-Columbian Mayan city in the Yucatán Peninsula, occupied from approximately 600 to 1200 CE with peak development under Toltec influence in the 9th–11th centuries. El Castillo (the Temple of Kukulkan) is a stepped pyramid 30 metres tall with 91 steps on each of its four sides; counting the upper platform yields 365, matching the Haab' solar year. On the spring and autumn equinoxes, the late-afternoon sun casts a serpentine shadow down the northern balustrade that connects to a carved serpent's head at the base. The Great Ball Court is the largest in Mesoamerica, 168 by 70 metres; an acoustic anomaly causes a single hand-clap at one end to produce nine distinct echoes. The Sacred Cenote, a 60-metre-wide natural sinkhole, has yielded human and ritual offerings dredged from its depths.

The pyramid is a calendar that performs once a year — and the ball court answers a clap nine times in a row.