Dunboy Castle is a ruined castle on the Beara Peninsula in south-west Ireland near the town of Castletownbere. It was a stronghold of the O'Sullivan Bere, a Gaelic clan leader and 'Chief of Dunboy', and was built to guard and defend the harbour of Berehaven. Its presence enabled O'Sullivan Bere to control the sea fisheries off the Irish coast and collect taxes from Irish and continental European fishing vessels sheltering in the haven. It was also a centre for the import/export trade to and from the continent. Today, much of the castle is destroyed but the ruins are open to the public.