One of the most important cathedrals in Mexico, dominating the south side of the Zócalo. The exterior is imposing rather than ornate — grey stone towers, a sober Herreran facade — but the interior is another world: vast, gilded, with an onyx altar, intricate choir stalls carved from dark wood, and a powerful Baroque organ that fills the nave during mass.
Worth attending a Sunday mass for the music as much as the architecture. Entry is free; the sacristy and treasury charge a small fee. The best views of the towers are from the far end of the Zócalo in the late afternoon, when the light catches the stone. A guide on the plaza can arrange a rooftop visit to the bell towers for a panoramic view of the city and, on clear days, the snow-capped cone of Popocatépetl.