The remains of the Castle can be visited
Grimmenstein Castle (Ruin) (St. Margrethen)

In 1254, the von Grimmenstein family first appears in documents with Konrad. This vassal of the Abbot of St. Gallen originally belonged to the von Falkenstein family and called himself "von Grimmenstein" since the construction of the eponymous castle. The von Falkenstein/von Grimmenstein family died out shortly before 1315.
Therefore, in 1315, the Abbot of St. Gallen handed over the castle to Baron Wilhelm von Enne from South Tyrol. He is said to have been expelled by the Habsburgs from his ancestral castle in what is now Montan, south of Bolzano.
Fate of the Castle
Under the von Enne family, Grimmenstein was involved in military conflicts at least three times: in 1361, it was conquered in a feud. In 1405, Appenzellers and St. Galleners partially destroyed it. After 1410, Georg II and Wilhelm VI von Enne rebuilt the castle. The brothers came into conflict with the city of Constance due to an attack on a ship. Georg II was arrested in Constance and brought to trial. In exchange for his freedom, he had to promise to destroy his castle. According to Aegidius Tschudi's chronicle, in 1416, more than sixty men were occupied for eight days with its demolition. The ruin then served as a quarry for a long time. With Georg II, the von Enne family died out in 1436.
Location and Appearance
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: 47.4528, 9.6129