Morelia is a UNESCO-listed colonial city built in pink cantera stone, and the best thing to do in it is walk — the cathedral, the aqueduct's two hundred and fifty arches, the Palacio Clavijero, the sweet shops of the Mercado de Dulces.
What makes it a base is the rest of Michoacán. The monarch butterfly sanctuaries are two to three hours east and run from late October to March. Pátzcuaro and its lake, with the island of Janitzio and the P'urhépecha villages around the shore, are an hour southwest, and are the heart of Mexico's Day of the Dead observance on the night of 1 November — book months ahead or do not try. Paricutín, the volcano that came out of a cornfield in 1943 and buried a village to its church steeple, is three hours west and reached on horseback from Angahuan.
Morelia's own calendar is worth checking: the Festival Internacional de Música in November and the film festival in October both fill the city.