The remains of the Castle can be visited
Mesocco Castle (Ruin)

One of Switzerland's largest castle complexes, the Mesocco Castle Ruin, stands on a prominent rock south of the village of Mesocco in the canton of Graubünden. For centuries, it served as the dominant center of the Misox Valley.
History+
The first documented mention of Castello Mesocco dates back to 1219. However, archaeological findings suggest settlement since the Neolithic Age, with an early medieval church castle from the 6th or 7th century as a presumed predecessor. The Barons of Sax established a medieval castle here, which for about 400 years was their ancestral seat and the starting point of their rule over Misox.
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: 46.3800, 9.2324