The real highlight of the 14th-century Gothic Augustinerkirche is not its pale, vaulted interior but the Herzgruft, a crypt containing silver urns with the hearts of 54 Habsburg rulers. The crypt is open on Sunday after the 11am Mass (celebrated with a full choir and orchestra) – turn up around 12.30pm. The church hosts regular evening classical music concerts; check schedules at http://hochamt.augustiner.at. Sometimes on a visit you can catch the choir practising. Many Habsburg weddings took place here.