The Castle can be visited
Charlottenhof Castle

In Potsdam stands Charlottenhof Palace, once the summer residence of Prussian Crown Prince Frederick William IV. It is distinguished by its Roman-inspired architecture and the personal involvement of the Crown Prince in its design.
History+
The history of the area where Charlottenhof Palace stands dates back to the 18th century. After changing hands several times, King Frederick William III acquired the land, which bordered Sanssouci Park to the south. At Christmas 1825, he presented it to his son, Crown Prince Frederick William, and his wife Elisabeth Ludovika of Bavaria. The Crown Prince then commissioned Karl Friedrich Schinkel to convert an existing manor house. Between 1826 and 1829, a small palace in the style of Roman villas was created with modest means, with Schinkel being supported by his student Ludwig Persius. The Crown Prince actively participated in the design of both the palace and the park.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Joachim Schneeleopard
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: 52.3956, 13.0256