The remains of the castle can be visited
Old Gleichen Castle

The castle ruin Alte Gleichen is on the southern of the two Gleichen mountains in Southern Lower Saxony.
History+
The origins of Alte Gleichen Castle date back to the early 12th century, when it was built around 1100 by the Counts of Reinhausen. After its construction, the complex changed hands several times until it came into the possession of the Lords of Uslar around 1270. This family later divided their property into the Altengleichen and Neuengleichen lines. Although the castle never fell by conquest, it was abandoned as early as the 16th century and gradually fell into disrepair, as its inhabitants moved to the surrounding supply farms.
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: 51.4672, 10.0385