The remains of the Castle can be visited
Altenstein Castle

Altenstein Castle Ruin, a medieval spur castle, stands on a mountain spur in the Eichsfeld district of Thuringia, above the upper valley of the Alte Hainsbach. It is now an accessible archaeological monument.
History+
The origins of Altenstein Castle are attributed to the Thuringian Landgraves, who expanded their dominion in the lower Werra valley in the late 12th century. The first documented mention occurred in 1329, when the Hessian Landgrave Heinrich II pledged the castle and surrounding villages to Knight Berthold Eselskopf and squire Hugo from the Mark. In 1346, the castle guards Bruno and Hertwig von Weberstedt were obliged by the Hessian Landgrave to maintain peace, as they were known for their raids. Rights to the castle changed hands in 1347 to Urban von Weberstedt and in 1375, through pledging, to Lippold von Hanstein. Hermann II, the Hessian Landgrave, reacquired the castle in 1379 and transferred it to the von Mänz family.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=2036
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: 51.2848, 10.0563