This island castle served as the primary residence of Sir Niall Garbh O’Donnell at the turn of the 17th century, playing a crucial role in the turbulent politics of Ulster during the Nine Years’ War and its aftermath. The fortress fell to Sir Henry Folliott in 1608 when Sir Cahir O’Doherty launched his ill-fated rebellion, marking another chapter in the decline of Gaelic power in Donegal.

Today, visitors who make their way to the island will find substantial remains hidden amongst the vegetation. The most prominent feature is a large bawn wall, roughly 2 to 3 metres high and 2 metres thick, which encloses nearly the entire island in a sub-rectangular area measuring 35 by 39 metres. Though sections have collapsed and trees now grow through the masonry, three defensive embrasures survive; the best preserved example on the south wall rises over 3 metres and contains three gun loops, with the side openings cleverly angled to defend the southwestern and southeastern approaches. A gateway in the centre of the north wall leads across a narrow neck of land to a small promontory where the foundations of what was likely the main keep can be traced amongst the fallen stones, though dense vegetation now obscures much of the original plan.

The castle has one peculiar claim to fame: in the 1840s, antiquarian Patrick Fagan recorded that a sheela-na-gig, one of those enigmatic female exhibitionist carvings found on medieval Irish buildings, had been removed from the island and built into the coach house wall at nearby Lougheask Castle. Despite searches in the 1980s, this carved figure remains missing, though a sketch preserved in the Ordnance Survey Memoirs provides tantalising evidence of this lost piece of medieval art. The ruins stand as a testament to the O’Donnells’ last desperate attempts to maintain their ancestral power in Donegal before the Plantation of Ulster transformed the landscape forever.