Danube
The Danube flows through many cities, including four national capitals (shown below in bold), more than any other river in the world. Ordered from the source to the mouth they are:
The Danube is navigable by ocean ships from the Black Sea to Brăila in Romania and by river ships to Kelheim, Bavaria, Germany; smaller craft can navigate further upstream to Ulm, Württemberg, Germany. About 60 of its tributaries are also navigable.
Regensburg Museum of Danube Shipping
The Regensburg Museum of Danube Shipping ("Donau-Schiffahrts-Museum Regensburg") is a maritime museum of river shipping on the river Danube and other rivers, sited in the town of Regensburg in Germany. It also contains art collections on that topic, along with material on boatmen's work and training. Its main exhibits are the steam tugboat "Ruthof / Érsekcsanád" and the diesel tug "Freudenau".