We visited the church during a free organ concert - something that seems to occur on a relatively daily basis at 3pm - and were treated to a glorious experience. The music was divine, consisting of an orchestra and choir besides the organ, and the paintings and architecture were beautiful. Visitors are given helpful information pamphlets and pictures were allowed - at least the time we visited! Offerings/donations were accepted but not required.
We were very glad that we made the time in our itinerary to include this. A definite must for music enthusiasts on a budget.