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

The ruins of Greifenstein Castle, a former hilltop castle whose origins date back to the 12th century, was once the center of power for a dominion in the Albula Valley.
History+
The construction of Greifenstein Castle is presumed to have occurred in the second half of the 12th century, although precise documentary evidence is lacking. It served as the ancestral seat of the noble free lords of Greifenstein, who were related to the Wildenbergers and Frauenbergers. In 1233, Rudolf von Greifenstein is mentioned, who was obliged to go on a crusade after his involvement in the murder of Bishop Berthold. Before 1300, the castle and its associated dominion passed to the Wildenbergers. In 1320, Hugo and Anna von Wildenberg pledged the castle to the Prince-Bishopric of Chur. After changing owners and conflicts, including with the Lords of Matsch, the castle was conquered by episcopal troops in 1394 and became the episcopal center in the Albula Valley.
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: 46.6759, 9.6929