Ex-Convento de San Gabriel
This impressive, huge, former convent includes a trio of churches. The most unusual is the Moorish-style Capilla Real, with 49 domes. Construction began in the 1540s, and the building was originally open on one side to facilitate the conversion of huge masses of people. A handful of Franciscan monks still live in one part of the premises, so be respectful of their privacy. La Biblioteca Franciscana (open weekdays 9 to 5) is a fascinating on-premises library of over 24,000 volumes from the 16th through 19th centuries, with occasional exhibitions.