St. Stephan's Cathedral is the centrepiece of Passau's old town, a magnificent Italian Baroque building whose white and grey facade rises above the narrow streets of the peninsula. The original Romanesque cathedral was destroyed in the fire of 1662; the replacement was built by Italian architect Carlo Lurago and decorated with stucco work by Giovanni Battista Carlone in a style that feels more like Rome than Bavaria.
The interior is overwhelming in the best sense — vaulted, gilded, and dominated at the west end by the enormous organ. At 11am on weekdays from May to October, a 30-minute organ concert is held, and the sound in the resonant nave is extraordinary. Check locally for current schedules and any concerts at other times. Entry to the cathedral is free; there may be a charge for the crypt.