Ackergill Tower, on the shores of Sinclair's Bay a short distance from Girnigoe Castle.

The "History of Ackergill Tower" at http://www.ackergill-tower.co.uk/ states: "In 1547, Queen Mary granted a remission to George, Earl of Caithness, from treasonably taking and holding the castle and for keeping the Captain--Alexander Keith-- a prisoner in nearby Castle Girnigoe. The Fifth Earl of Caithness took Ackergill Tower by force in the late 1600's and held it for several years until Cromwell's troops in 1671 sent the Earl scurrying for safety in Orkney."