Amazing architecture and art
The Metropolitan Cathedral is a must if you visit Mexico City. Construction and decoration took nearly 3 centuries (1573-1656).
The cathedral is host to a mixture of styles, a result of being built over such a long period of time. Hernán Cortés and the other conquistadores used the stones from the destroyed temple of the Aztec god of war Huitzilopochtli, main deity of the Aztecs, to build the cathedral. The cathedral has four facades with portals flanked by columns and statues. The two bell towers contain a total of 25 bells. Fourteen of the cathedral's sixteen chapels are open to the public. There are amazing ornate altars, altarpieces, retablos, paintings, furniture and sculptures.
The cathedral is home to two of the largest 18th century pipe organs in the Americas. My advise is to visit in the afternoon, because there are two masses in the morning, and access is blocked either to the front or the rear of the cathedral. But if you would like to experience the sound and vibrations of the organ, go in the morning. Casual apparel is OK, but remember that you will be entering a conservative religious site, so keep in mind that you have to be respectful. If you are not, one of the many security guards will remind you.