This five-storey tower house, likely built during the reign of James I in the early 17th century, once served as a formidable residence for the O’Brien family of Coonagh. When surveyed in 1840, observers noted its castle-like appearance with distinctive barbicans at the corners; a design that placed it amongst the last generation of Irish tower houses. The structure originally measured approximately 11 metres along its west side and 14 metres along the south, with impressively thick walls of around 2 metres that have partially withstood the test of time.

Though the east and north sides have largely crumbled away, the remaining west and south walls preserve fascinating architectural details that reveal the building’s sophisticated design. Each of these surviving walls is crowned with chimney stacks, whilst the northwest corner still displays a circular bartizan perched on pyramidal corbels. The tower featured unvaulted rooms across four main storeys plus an attic level, with mullioned windows that would have flooded the interior with light. A spiral staircase once wound through the southeast corner, and additional chambers were built into the thickness of the east wall, maximising the living space within the fortress-like structure.

The castle’s documented history reveals its changing fortunes through Ireland’s tumultuous past. During the Desmond Rebellions, it was held by Moriert Mergagh, who died in the conflict. By 1617, the Hurley family of Knocklong had taken possession, with Sir Maurice Hurley, described as an ‘Irish Papist’, maintaining the castle in good repair along with an associated mill through the 1650s. Following the Cromwellian conquest, the property passed to Edmund Harrison before being transferred in 1667 to the trustees of Erasmus Smith’s charity schools. The 1657 Down Survey map shows the castle standing beside a medieval road that connected it to nearby Coonagh Castle, with a cluster of dwellings gathered close by, suggesting it remained an important local landmark even as its military significance waned.