The remains of the castle can be visited
Hasenburg Castle
The imperial castle ruin Hasenburg, also known as Asenberg or Asenburg, is in Thuringia. Its remains range from prehistoric settlements to medieval conflicts.
History+
The Hasenburg was an imperial castle whose origins date back to the Hallstatt period, when the mountain already hosted a fortified hilltop settlement. From the 7th century onwards, the Franks used the site as a border fortress against the Saxons. In the High Middle Ages, the castle played a role in the conflicts between King Henry IV and the rebellious Thuringians and Saxons. It was part of a fortification system to secure royal property and strengthen royal power.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Hasenburg,_Burgtor_%282000%29.JPG
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: 51.4490, 10.4872