The Castle can be visited
Prinzenhaus Castle

The Prinzenhaus in Plön, Schleswig-Holstein, is a former garden palace in the park of Plön Castle. It is the only surviving pleasure palace of its kind in the state and earned its name because it served as a residence and school for the sons of Emperor Wilhelm II in the late 19th and early 20th centuries.
History+
The origins of the Prinzenhaus date back to the expansion work on Plön Castle, commissioned by Duke Friedrich Karl of Schleswig-Holstein-Plön from 1730. As part of this transformation of the castle into a Baroque residence, a modern garden complex was also conceived. Since the garden could not be directly aligned with the castle, a pavilion was built from 1744. This pavilion, constructed between 1744 and 1751 under the direction of Johann Gottfried Rosenberg, served as a private pleasure palace for the Duke and his wife. After the Duke's death in 1761, the duchy fell to the Danish royal house. The garden house then largely stood empty, and the park became overgrown. From 1782, it served as a residence for the family of the royal Danish master hunter Andreas Gottlieb von Rosen. In the mid-19th century, the park was transformed into an English landscape garden.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://schloesserrundschau.de/schleswig/schloesser/ploen02.html
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 54.1541, 10.4091