The remains of the Castle can be visited
Osterburg Castle

The Osterburg castle ruin, a former hilltop castle, is situated at an elevation of approximately 699 meters near Bischofsheim an der Rhön in the Bavarian district of Rhön-Grabfeld. Its history presumably dates back to pre-Christian times and is marked by many unsolved mysteries.
History+
The origins of the Osterburg are presumed to be in Celtic antiquity, possibly as a refuge castle around 1000 BC. It is believed to have later passed into Germanic possession and may also have been a Merovingian or Carolingian fortification. In the 6th century, it allegedly served as a hunting lodge for a Frankish ruler. Later, the castle protected the lands of the Würzburg prince-bishops against the prince-abbots of Fulda. Around 1200, the first nobles, such as Reinhold von der Osterburg, were mentioned.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Joachim Schneeleopard
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: 50.4001, 9.9819