Notre Dame Cathedral, Paris, France
Every Sunday morning at 10am in the Cathedral at Notre Dame in Paris they have a Gregorian Mass. As you can imagine, this massive Gothic church has amazing acoustics, adding to the atmosphere of the Sunday Gregorian service. I'm sure I reserved my one way ticket to the perpetual inferno since I kept wondering how Led Zeppelin would sound in this perfect auditory setting.
Pro tip: If you go to Notre Dame, after you finish seeing the inside, line up around the corner to climb to the top. The claustrophobic climb is worth it to see the gargoyles up close. Time your visit so you can be on the catwalk when the bells chime.