This O’Clery stronghold, protected by cliffs to the north and south and a steep drop to the sea on its western side, was destroyed in 1390 according to the Annals of the Four Masters. By the time of the Civil Survey in 1654-6, it was already noted as ‘the ruined walls of an Old Castle’, having passed into the ownership of one Francis Brassy. The castle’s defensive position was enhanced by a deep fosse, or ditch, cut across the eastern approach; its western side reinforced with stone facing that both strengthened the defence and supported the curtain wall above.

What remains today are mainly the lower courses of walls, with the most substantial surviving structure being the gatehouse keep that once guarded the entrance passage. This keep, though much reduced from what existed in the early 1900s when antiquarian Lockwood documented the site, still shows fascinating architectural details including a projecting garderobe whose shaft discharged over the northern cliff face. The ground floor was divided into three chambers, with the northeastern room featuring a deeply splayed arrow loop and a doorway complete with its original drawbar hole. Hugh Allingham, writing in 1879, mentioned traces of an underground passage within the keep, though this has long since been blocked and lost to view.

The courtyard once contained at least two additional buildings; one at the southeast corner survives as two wall sections standing about five metres high, whilst another at the southwest corner is now reduced to a single angle of masonry less than two metres in height. Sections of the curtain wall have collapsed into the fosse, and much of the site is now defined by modern drystone walls. Though the visible remains are clearly medieval, the strategic importance of this precipitous promontory may well have attracted earlier inhabitants, making Kilbarron a site where layers of history potentially stretch back beyond its documented medieval origins.