Santa Catalina Monastery is a city within a city, a massive 20,000 square meter complex with streets, plazas, and houses. Founded in 1580, it remained closed to the outside world for 400 years until 1970. The vibrant blue, orange, and red walls reflect colonial life where wealthy Spanish families sent their second daughters to become nuns. About 20 nuns still live in a private section. Night candlelight tours offer a magical atmosphere.