Altenstein Palace

Schloss Altenstein is a schloss, or palace, upon a rocky hill on the south-western slope of the Thuringian Forest, not far from Eisenach, Thuringia, Germany. It was the summer residence of the Dukes of Saxe-Meiningen, and is surrounded by 160 hectares of English landscape garden, which contain, among other objects of interest, a cavern 300 metres long, through which flows a large and rapid stream.

Source: Wikipedia