This O’Sullivan stronghold, reputedly built around 1540 by Dermot O’Sullivan, consists of a tower house nestled within the southwest corner of a rectangular bawn, or fortified enclosure. The tower’s western wall stretches 10.3 metres wide, with most of the northern wall extending 12 metres, and these walls still stand four storeys high. Inside, you can trace the ghostly outlines of segmental vaults that once covered the first and third floors, their east-west axis still visible on the western face. The tower features central window openings on each level of the west wall, with the first floor embrasure particularly notable for its mural passages on either side, whilst the third floor sports a single ogee-headed window light.

The bawn itself forms a rough rectangle measuring 26 metres north to south and 48 metres east to west, with projecting towers at each corner; its southern face dramatically overlooks a rock-cut gorge. This defensive enclosure appears to be a later addition, likely dating to the 17th century. The eastern half has been altered to accommodate farm buildings, now abandoned, whilst the western wall and the original western end of the northern wall bristle with gun loops. The corner towers show interesting defensive features: the northeast and southeast towers have acutely angled outer faces reminiscent of bastions on star-shaped forts, the northwest tower presents a more blunt point, and the southwest tower takes a roughly rectangular form. Intriguingly, the southwest tower contains four tiers of nesting boxes on each face at first floor level, suggesting the castle’s defenders may have kept pigeons for food or communication.

The castle’s history is tied to the turbulent politics of early 17th century Ireland. After holding out against English forces, Carriganass finally surrendered in 1602 following the fall of Dunboy Castle, marking the end of O’Sullivan resistance in the region. Today, matching bartizans crown the northwest and southwest corners of the tower, each supported by a corbel on adjoining walls with a straight face set across the corner, whilst small mural chambers and passages at various levels hint at the complex internal layout that once served the castle’s inhabitants and defenders.