The remains of the Castle can be visited
CastleRübeland (Oberharz am Brocken)
Birkenfeld Castle

The Historic Birkenfeld Castle+
A Glimpse into the History of Birkenfeld Castle+
Birkenfeld Castle, a venerable edifice steeped in history, was first documented in 1134 as being in the possession of Knight Werner von Birkenfeld. This early mention underscores the castle's long-standing significance in the region.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Roland Neubert, Halle (Saale)
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: 51.7532, 10.8428