Thuisbrunn Castle, Medieval castle ruins in Gräfenberg, Germany.

Thuisbrunn Castle is a castle ruin in Grafenberg in Upper Franconia, with preserved stone walls that include a visible bergfried tower and remains of administrative buildings within the fortified area. The complex sits on an elevated position and shows how larger and smaller structures were arranged together on the site.

The fortress was first documented in 1348 and subsequently experienced multiple destructions during regional conflicts. Military events such as the War between Cities in 1388 and the Second Margrave War in 1553 inflicted severe damage on the structure.

The castle's name comes from the village of Thuisbrunn, first recorded in 1348 with Lord Hiltpolt of Mayenthal as Burgherr. Since 1961 the site has been in private ownership, and the former Vogtei office, built in 1667, later served as a forestry office. Visitors can see the bergfried and the Vogtei building, the only structures rebuilt after 1553.

The site sits on a hill and is reachable from the paths running through Thuisbrunn village in the municipality of Grafenberg. Walking to the ruins is possible on local trails and provides different vantage points to view the complex from various angles.

The castle's oldest surviving structure is the bergfried, rebuilt by 1558 after its destruction in 1553; the Vogtei building replaced the Amtshaus in 1667. In 1816 cartographer Johann Christoph Stierlein produced the first precise map of the castle area and its remaining buildings. The site was shelled by American troops near the end of the Second World War and passed into private ownership in 1961.