The castle’s strategic position made excellent use of natural defences; sheer cliffs guard the north and south approaches, whilst the western side drops steeply towards the sea. Only the eastern approach required human intervention, where a defensive fosse (or ditch) was cut north to south across the neck of the promontory. The western face of this fosse was lined with stone, both reinforcing the defences and providing support for the curtain wall above.

What remains today are mostly foundation courses and lower walls, with the exception of two wall sections in the southern building that rise to about five metres. The entrance to the castle lay on the eastern side, where remnants of a gatehouse keep can still be traced north of the passage. Evidence suggests there may have been a drawbridge arrangement at the western end of the causeway crossing the fosse. The courtyard once contained at least two buildings; one at the southeast corner, now reduced to wall fragments and footings, and another at the southwest corner, though only its southwestern angle survives to any height.

Whilst these ruins clearly date to the medieval period, the castle’s documented history is surprisingly sparse. We know it was destroyed in 1390, as recorded in the Annals of the Four Masters, and by the 1650s the Civil Survey describes it simply as ‘the ruined walls of an Old Castle called Kilbarron’ belonging to one Francis Brassy. The promontory’s commanding position and natural defences suggest it may well have been occupied long before the medieval castle was built, though no earlier structures have been definitively identified amongst the surviving stonework.