Wilhelmstein castle is the ruin of a castle in the valley of the river Wurm. 

From 1265 to 1269, Count Wilhelm IV of Jülich built the castle named after him. It was mentioned in writing for the first time in 1344.

The castle was built as a refuge fort. The population from the nearby fief could find shelter there in times of emergency.

The castle now houses a free-standing stage and a restaurant. In the summer months it serves as a venue for concerts, cabaret and cinema.

In the picture the terrace of the restaurant can be seen. From there you have a very nice view over the valley of the river Wurm.

source:

https://de.wikipedia.org/wiki/Burg_Wilhelmstein

http://www.burgwilhelmstein.de/die-burg-wilhelmstein/