This small island fortress served as a principal stronghold for the O’Donnells, one of Ulster’s most powerful Gaelic families, with Sir Niall Garbh O’Donnell making it his chief residence around 1601-1602. The castle’s strategic importance became evident during Sir Cahir O’Doherty’s revolt in 1608, when Sir Henry Folliott successfully captured the island, marking another chapter in the turbulent transition from Gaelic to English rule in Ulster.

Today, the tree-covered island reveals the substantial remains of this once-formidable fortress. The most impressive feature is a large bawn wall, roughly 2 to 3 metres thick and up to 3 metres high in places, which encloses an almost rectangular area measuring 35 by 39 metres; effectively encompassing nearly the entire island. Despite centuries of neglect and trees growing through the masonry, visitors can still identify three embrasures in the walls, with the best-preserved example on the south wall standing over 3 metres high. This particular embrasure contains three gun loops; one facing directly outward and two set diagonally to defend the southwestern and southeastern approaches, showing the sophisticated military planning of the period.

The northern section of the castle complex reveals additional defensive features and structures. A gateway in the centre of the north bawn wall leads across a narrow neck of land to a small promontory, where the foundations of what was likely the main keep can be found amongst fallen masonry and vegetation. The builders added a secondary wall against the outer face of the north bawn wall for extra protection, whilst the remains of what may have been a boat landing structure can be seen on the eastern side of the neck. An intriguing historical footnote comes from 1846-7, when antiquarian Fagan recorded that a carved female exhibitionist figure, once part of the island castle, had been removed to nearby Lougheask Castle’s coach house, though this carving has since disappeared despite searches in the 1980s.