Chichén Itzá is a Maya city in the flat limestone scrub of Mexico's Yucatán, built around a pyramid that answers when you clap at it. One clap at the foot of El Castillo's northern staircase comes back as a sharp chirp, matched by acousticians to the call of the quetzal, the bird the Maya held sacred. The pyramid has 365 steps, one for each day of the year, and twice a year it proves the point. On the March and September equinoxes the late sun cuts seven triangles of shadow down the northern balustrade, down to a carved stone snake head at the base. The lawn fills hours beforehand, tens of thousands deep, though it shows faintly for a day or two either side, to a fraction of the crowd.
A short path off the plaza ends at the Sacred Cenote, a sinkhole with sheer sides. Yucatán has no rivers; its water runs underground and surfaces only where the rock roof falls in. Into this one the Maya dropped gold, jade and, the excavations say, people, for Chaac, the rain god. There is water under the pyramid too: a 2015 survey found a flooded cenote twenty metres across beneath the foundations, so it was most likely raised over a sacred sinkhole on purpose. It is not solid above ground either: an older pyramid stands inside it, and tunnelling in the 1930s reached a buried temple with a red-painted jaguar throne, jade discs for its eyes. The city keeps working on you at ground level. The Great Ball Court is the largest in the ancient Americas: 135 metres between eight-metre walls carved with the game and the fate of the losing captain. A sound made at one end carries clearly to the other. Beside the Temple of the Warriors stand rows of pillars, each carved with a different warrior; El Caracol, a round tower, tracks Venus through slit windows. You cannot climb the pyramid any more, and it costs you nothing: the serpent comes twice a year, but the chirp answers anyone who stands at the bottom and claps.