The remains of the Castle can be visited
Schwarzenstein Castle (Ruin) (Obersaxen)

The Schwarzenstein ruin in Obersaxen, Graubünden, is a historic castle ruin. It is part of the settlement history of the region, where German-speaking settlers encountered Rhaeto-Romanic territory.
History+
The exact history of the construction of Schwarzenstein Castle is not documented in written records. It is believed to have been founded by the Barons of Rhäzüns and was first mentioned as their property in 1289. The castle played a role in property disputes in Obersaxen, necessitating the presence of Rhäzüns retainers. An example of this is the feud in which Heinrich von Löwenstein lost the castle to Heinrich Brun von Rhäzüns but was later supposed to return it. The masonry suggests a construction around the mid-13th century. The complex was probably rebuilt and extended twice. Schwarzenstein was likely abandoned in the mid-14th century after the Walser settlers received lower jurisdiction and the Rhäzüns ministerials were no longer needed. In 1468, only a farm called Schwarzenstein was mentioned.
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: 46.7502, 9.0727