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.
Danube
Also, leisure and travel cruises on the river are of significance. Besides the often frequented route between Vienna and Budapest, some ships even go from Passau in Germany to the Danube Delta and back. During the peak season, more than 70 cruise liners are in use on the river, while the traffic-free upper parts can only be discovered with canoes or boats.