The Castle can be visited
Tenneberg Castle

In Waltershausen, Thuringia, stands Tenneberg Castle, once a medieval fortress and later a hunting lodge for the Dukes of Gotha. Today, it houses a museum.
History+
The origins of Tenneberg Castle date back, possibly to the 6th century, when the castle hill was already fortified with an earthwork. The first documented mention of the medieval castle occurred around 1176 under the Thuringian Landgraves, who used Tenneberg as a secondary residence. Duke Johann Casimir transformed it into a hunting lodge, and from 1640 to 1646, it temporarily served as a residence for Ernst I. His successors also used Tenneberg as a summer residence.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=589&sid=9b2b210ff3d27b7a80b9c70dbb4777c0
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: 50.8956, 10.5522