Twice a year the great pyramid of Chichén Itzá seems to move: on the spring and autumn equinoxes, the late-day sun sends a serpent of shadow rippling down its northern staircase to meet a carved stone snake-head at the base. The pyramid is El Castillo, a 30-metre monument to the feathered serpent god Kukulkán, and it is built as a calendar — 91 steps on each of four sides plus the top platform make 365, one for every day of the year. El Castillo was the ceremonial heart of one of the largest Maya cities, which peaked between roughly the 8th and 12th centuries, blending Maya tradition with styles shared across central Mexico. Around it stand the Great Ball Court, the largest in the ancient Americas, the colonnaded Temple of the Warriors and the round observatory of El Caracol — a UNESCO World Heritage Site since 1988 and one of the New7Wonders of the World.
Arrive at the 8am opening, before the tour buses from Cancún and Mérida fill the plaza, and El Castillo commands the cleared ground alone. You can no longer climb it — the stairs were closed in 2006 after a visitor fell to her death — so the city is read from below: the carved columns of the Temple of the Warriors, the sheer limestone rim of the Sacred Cenote where the Maya once threw gold, jade and human offerings to the rain god, and the ball court's high walls. Stand at the foot of the staircase and clap once, and a sharp chirp answers back — an echo acousticians have matched to the call of the sacred quetzal bird. Today the site draws well over a million visitors a year, and on each equinox tens of thousands gather on the grass to watch the shadow-serpent descend.