The San Agustin museum is absolutely amazing and a site you must see if visiting Manila. The San Agustin museum is located in Intramuros, also known as the walled city. You can find the museum located right next to the San Agustin Church. The museum is open every day from 8 a.m. until 6 p.m. and closes for lunch from noon until 1 p.m. You can visit the church and the museum for free.
However, donations are accepted and usually expected. You should donate when visiting because everything they receive is only from donations. You cannot take your camera inside of the museum, but there are hallways and specific rooms where photos can be taken.