To be privately owned
Skibo Castle

West of Dornoch in the Highland region, Skibo Castle is a historic castle in Scotland. Originally built as a bishop's residence, it later gained note through the industrialist Andrew Carnegie, who transformed it into an estate.
History+
Skibo Castle dates back to 1186, when it was built by Gilbert de Moravia, the Bishop of Caithness. Until 1545, it served as a bishop's residence. In 1745, the estate passed into the possession of Robert Gray. A descendant initiated a renovation of the castle in 1760. After this period, ownership changed hands frequently until Evan Charles Sutherland-Walker acquired the property in 1872.
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: 57.8731, -4.1323