Chichén Itzá is the most impressive Maya site on the Yucatan Peninsula and one of the New Seven Wonders of the World. The massive pyramid of El Castillo, the Great Ball Court, the Temple of Warriors, and the sacred cenote make for a day of intense archaeological richness. The site is about 200 km west of Playa del Carmen — two and a half to three hours by bus from the ADO terminal.
Go early. Coaches from Cancun dump thousands of day-trippers at the site mid-morning, and the heat by noon is fierce. A 7am or 8am bus from Playa puts you at the ruins as they open. The town of Valladolid, an hour west of the ruins, makes a good midday stop for lunch before returning; it has colonial architecture and a cenote right in the town square.