Danube
Classified as an international waterway, it originates in the town of Donaueschingen, in the Black Forest of Germany, at the confluence of the rivers Brigach and Breg. The Danube then flows southeast for about , passing through four capital cities (Vienna, Bratislava, Budapest and Belgrade) before emptying into the Black Sea via the Danube Delta in Romania and Ukraine.
Danube Valley Railway (Baden-Württemberg)
The Danube Valley Railway runs alongside the Danube river and crosses it several times. From Immendingen the line runs across the Upper Danube Nature Park "(Naturpark Obere Donau)", brushing up against the southern edge of the Schwäbische Alb, all the while following the course of the Danube. Between the towns of Inzigkofen and Herbertingen, the Danube Valley Railway again shares its tracks, this time with the Zollernalb Railway. At Ehingen (Donau), the line leaves what is known as the Danube valley today, and follows the valley formed by the Danube in times past, along the rivers Schmiech, Ach, and Blau. The railway again touches the border of the Schwäbische Alb between Allmendingen and Blaustein, and meets its eponymous river again at the line's terminus in Ulm.