Dunoon Castle is a ruined 12th century castle located at Dunoon on the Cowal Peninsula in Argyll and Bute, Scotland. The castle sat upon a cone-shaped hill about 80 feet high. The castle was a royal residence in the 14th century, and in the 17th century fell into ruins. The castle originally belonged to the Lamont family but became a royal castle with the Earls of Argyll (Campbells) as hereditary keepers, paying a nominal rent of a single red rose to the sovereign.