Passau, a German city on the Austrian border, lies at the confluence of the Danube, Inn and Ilz rivers. Known as the Three Rivers City, it's overlooked by the Veste Oberhaus, a 13th-century hilltop fortress housing a city museum and observation tower. The old town below is known for its baroque architecture, including St. Stephen's Cathedral, featuring distinctive onion-domed towers and an organ with 17,974 pipes.
