The historic centre, the Aztec ruins, the Diego Rivera murals, and the world-class Anthropology Museum will keep most travellers busy for several days. Beyond the obvious, the great pleasure of Mexico City is wandering its neighbourhoods — colonial Centro Histórico, leafy Roma and Condesa, village-like Coyoacán and San Ángel, monumental Polanco — each with its own pace and personality.
The Zócalo, the Cathedral, the Templo Mayor, the Palacio Nacional with its Rivera murals, and the Palacio de Bellas Artes are the unmissable core of the centre. A second tier — Chapultepec Castle, the Soumaya and Jumex museums in Polanco, the Casa Azul and Trotsky house in Coyoacán, the Anahuacalli pyramid in the south, Luis Barragán's house in Tacubaya — extends easily to a week. For a third trip, allow time for the UNAM campus, the Basilica of Guadalupe in the north, the Mercado de la Merced, and a Sunday boat ride at Xochimilco.
Mexico City sits at 2,240 metres. Arrive a day early, drink more water than you think you need, and pace the first two days slowly until you adjust.