The remains of the Castle can be visited
Wartenstein Castle (Ruin) (Pfäfers)

On a steep rock outcrop high above the Rhine Valley in Switzerland lies the Wartenstein ruin, a former hilltop castle. Its name means “stone from which one keeps watch.”
History+
The origins of Wartenstein Castle date back to 1206, when it was built on behalf of Konrad von Zwiefalten, the abbot of the Imperial Abbey of Pfäfers. It was first mentioned in 1208 when Emperor Otto IV pledged the protective vogtei over the monastic estates to Heinrich von Sax, before it passed to Heinrich von Falkenstein in 1210. In 1257, Abbot Rudolf III of Bernang repurchased the vogtei for 300 marks of silver from the Empire and the von Sax family. Later, in the 14th century, the Counts of Werdenberg-Heiligenberg assumed the role of monastic vogts. A reconstruction and restoration took place in 1341 under Abbot Hermann II of Arbon, during which a chapel was also built within the fortress. Around 1430, Wartenstein served as a residence for Abbot Gerold von Eroltzheim.
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: 46.9931, 9.5104