Teotihuacan is laid out along a single great axis, the Avenue of the Dead, which runs four kilometres from north to south. At the north end stands the Pyramid of the Moon, facing the Avenue and the sacred mountain of Cerro Gordo behind. Halfway along, the Pyramid of the Sun — the largest in Mesoamerica — looms to the east. At the south end is the great walled enclosure of the Ciudadela, with the Temple of the Feathered Serpent inside it.
The big pyramids are unmissable but the city's residential and palace compounds are where the murals and decoration survive. The Palace of Quetzalpapálotl by the Pyramid of the Moon, the Tepantitla compound with its great paintings, and the apartment complexes of Atetelco and Tetitla reward an hour each. The site museum is small but excellent.
Start early, bring water and a hat, and budget a full day. Climbing the Pyramid of the Sun is currently restricted following recent stabilisation work — check on arrival.