The 3 Best Landmarks in Mexico City

The largest cathedral in the Americas, built over three centuries directly on top of the Aztec sacred precinct — you can literally watch it sinking unevenly into the old lakebed. Entry is free; paid extras include crypt/catacomb tours (150 pesos) and occasional bell tower visits. It's a working church, so dress respectfully and skip visits during Mass unless you're attending.

One of the largest city squares on earth, and the layered heart of Mexico for 700 years — Aztec ceremonial center, colonial Plaza Mayor, and today's stage for concerts, protests, ice rinks and Day of the Dead ofrendas. It's free, always open, and flanked by the Cathedral, Palacio Nacional and Templo Mayor. Come at least twice: once by day, once when the giant flag comes down at dusk.

Mexico's marble opera house: Art Nouveau outside, Art Deco inside, crowned with murals by Rivera, Orozco and Siqueiros — including Rivera's famous remake of the mural Rockefeller destroyed. The lobby is free; the mural-museum floors cost 90 pesos (free Sundays). If you can, see the Ballet Folklórico (Wed/Sun) to watch the Tiffany glass 'curtain' in action.