To be privately owned
Dunstaffnage Castle

In Dunbeg, Scotland, Dunstaffnage Castle, a ruin, stands on a rock plate. This fortress, once a center of power, offers a glimpse into Scottish history and architecture.
History+
The origins of Dunstaffnage Castle date back to around 1220, when Duncan Dubhgall, a descendant of Earl Somerled, had the fortress built for the MacDougall clan. Its location on the Firth of Lorne made it a stronghold. In 1309, the castle fell to Robert the Bruce and remained in royal hands. A notable episode occurred in 1746 when Flora MacDonald was imprisoned here after aiding Bonnie Prince Charlie in his escape following the Battle of Culloden.
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: 56.4548, -5.4376