The Castle can be visited
Stolberg Castle

Stolberg Castle is a historical structure in the South Harz region, on a mountain sloping on three sides above the town of Stolberg.
History+
The origins of Stolberg Castle date back to the 13th century, with its oldest preserved part, a round tower, dating to around 1200. Between 1539 and 1547, the castle underwent Renaissance-style expansions. Its current appearance was largely shaped by renovations carried out between 1690 and 1700. The southeast wing houses the neoclassical Grand Reception Room and the Red Hall, designed according to plans by Karl Friedrich Schinkel. Until 1945, the castle was owned by the Princes of Stolberg-Stolberg. After 1947, it served as an FDGB holiday home, leading to structural alterations.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Gottfried Hoffmann
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: 51.5749, 10.9540