Built probably in the 15th century, this rectangular tower measures 16.8 metres east to west and 12.8 metres north to south, though only its ground floor survives today, reaching a maximum height of 4 metres. The castle’s defensive features remain visible: a door at the northern end of the east wall leads to straight mural stairs rising towards the southeast corner, whilst central window openings pierce the north, south and west walls, their embrasures covered by segmental vaults. Practical medieval necessities are evident in the garderobe shafts built into the north and west walls.

The castle’s tumultuous history becomes clear through its architectural layers. A bawn wall extends from the south of the tower, running 75 metres eastward before turning north for another 55 metres. In 1602, during a siege that left the castle in ruins, defenders hastily constructed a secondary bawn with salient angles close to the tower; a desperate attempt to strengthen their position. This wasn’t the end of military activity at Dunboy; in the mid-17th century, a star-shaped fort was built on the site, adding another chapter to this contested ground.

Archaeological excavations conducted by Fahy between 1967 and 1973 have revealed much about the castle’s structure and evolution. The work uncovered the full extent of the medieval fortress and its later modifications, providing valuable insights into both the O’Sullivan Beare clan’s power base and the broader patterns of conflict and control in West Cork. Today, visitors can explore these excavated remains and trace the story of a castle that witnessed some of Ireland’s most dramatic historical moments, from clan warfare to the upheavals of the 17th century.