The remains of the Castle can be visited
Castelmur Castle

In the Bregaglia Valley, in the Swiss Alps of the canton of Graubünden, the Castelmur castle ruin is on a rock ridge. This complex once served as a valley barrier.
History+
The origins of the Castelmur valley barrier date back to 831, when it was first mentioned in a document as a fief. In 960, the Bregaglia Valley, including the fortress, came into the possession of the Diocese of Chur through an exchange, which was confirmed by Emperor Otto III in 988. Around 1121, the Chiavenners conquered the castle, but Pope Calixt II demanded its return. The Lords of Castelmur, a ministerial family named after the castle, managed the complex from 1190 on behalf of the Bishop of Chur. In the 14th century, the castle was repeatedly pledged, including to the von Planta family.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Castelmur_Lage.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: 46.3396, 9.5617