09:00, when it is quietest and before the square fills
Plan on about 60 minutes for both churches
The cathedral church of the first metropolitan see in the Americas, and the natural first stop. Work began in 1573 and did not finish until 1813, so the building is a record of two and a half centuries rather than one design. Two altarpieces carry it: the Altar of Forgiveness closing the choir in the middle of the nave, and the Altar of the Kings filling the apse, carved between 1718 and 1737 and among the earliest churrigueresque work anywhere in the Americas. Before you leave, walk round to the Sagrario Metropolitano attached to the eastern flank. It is a separate parish church with its own door and one of the finest carved fronts in Mexico, and most visitors walk straight past it.
Give your time to the Altar of the Kings in the apse, the Altar of Forgiveness at the choir, the slope of the floor, and the Sagrario next door.
Free to enter; tower and crypt access is ticketed and guided. The cathedral closes to sightseeing during Mass. Confirm current arrangements on the cathedral's official site.