The remains of the Castle can be visited
Seeburg Castle (Ruin) (Hartershausen)

The Seeburg Ruin, also known as Hartershausen Castle or Old Wall, is a hilltop castle ruin near Hartershausen, a district of Schlitz in the Vogelsbergkreis. It sits on an elevated position in front of the Seeberg.
History+
The origins of the Seeburg likely date back to the 12th century, when it was presumably built to protect the possessions of Fulda Monastery. The Lords of Schlitz, a ministerial family of the Imperial Abbey of Fulda first documented in 1116, are considered potential builders. The castle's sphere of influence probably included Hartershausen, as well as the villages of Hemmen and Üllershausen. The Seeburg was destroyed in the 13th century, an event attributed to Bertho II von Leibolz.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 50.6329, 9.5671