The remains of the Castle can be visited
Alt-Wartenberg Castle

On the wooded summit of Wartenberg, the northernmost Hegau volcano, lies the Alt-Wartenberg castle ruin. It was once the seat of the Lords of Geisingen, who later named themselves "von Wartenberg" after the castle and were an influential noble family in the region.
History+
The first documented mention of a family member, "Cono miles de Gisingen," dates back to February 2, 1095. The castle itself, a residential tower built in 1140 from basalt ashlar with walls over three meters thick, was surrounded by a curtain wall still five meters high today. In the 13th century, a new castle was built only about 100 meters to the east on the mountaintop. The "Old Castle" fell into ruin in the 15th century; it may have been abandoned in favor of the new complex.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Burg_Wartenberg3.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: 47.9258, 8.6139