The Schwarzwaldbahn or Black Forest Railway is a 149.1 km line that connects Singen and Offenburg, although publicity as in this poster usually refers to a beginning from the vacation town of Konstanz.
In the area between Triberg and Hornberg there are some impressive curves and twists and this scene probably depicts that terrain.
It's definitely a railway to travel over when in Germany. Info
The poster below shows a single track viaduct so may be intended to depict the Hollentalbahn which connects to the Schwarzwaldbahn at Donaueschingen, likewise highly recommended.