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.

Linz is a city in Upper Austria, straddling the Danube River midway between Salzburg and Vienna. Baroque buildings, including Old Town Hall (Altes Rathaus) and the old cathedral or Alter Dom, ring Hauptplatz, the old town’s main square. The riverside Lentos Kunstmuseum Linz has a major modern art collection. Across the river, the striking Ars Electronica Center focuses on society, technology and life in the future.

Bratislava, the capital of Slovakia, is set along the Danube River by the border with Austria and Hungary. It’s surrounded by vineyards and the Little Carpathian mountains, crisscrossed with forested hiking and cycling trails. The pedestrian-only, 18th-century old town is known for its lively bars and cafes. Perched atop a hill, the reconstructed Bratislava Castle overlooks old town and the Danube.

Budapest, Hungary’s capital, is bisected by the River Danube. Its 19th-century Chain Bridge connects the hilly Buda district with flat Pest. A funicular runs up Castle Hill to Buda’s Old Town, where the Budapest History Museum traces city life from Roman times onward.