This early fourteenth-century fortress, likely built around 1300 by descendants of the Carew family, forms an impressive square with walls reaching six metres high and over two metres thick. The castle’s roughly square courtyard, measuring about 26 by 25 metres internally, was once enclosed by ranges of buildings on all four sides, though local tradition holds that the structure was never actually completed. Historical accounts differ on whether a moat ever surrounded the castle; an 1835 description mentions one that had been filled in, whilst an earlier account from 1793 states no moat existed at all.

The castle’s defensive features reveal sophisticated medieval military architecture. Four latrine towers project from the curtain walls, with three containing double garderobe chutes and one with a single chute, providing a rather impressive total of seven toilets for the castle’s inhabitants. The walls are punctuated by cruciform arrow loops with expanded terminals, particularly concentrated on the north and east walls, allowing defenders to provide flanking fire along the external faces. The main entrance on the western wall once featured a portcullis slot and evidence suggests there may have been an external drawbridge, with tie stones indicating a possible gatehouse or forebuilding that protected the entrance. A spiral staircase just inside the gateway provided access to the upper floors and western range of buildings.

Archaeological evidence points to a grand residential complex within these formidable walls. A large double fireplace in the north wall marks the likely location of the Great Hall, whilst foundations of cellars and numerous embrasures, windows, and garderobes indicate substantial ranges of buildings lined all four sides of the courtyard. The construction techniques, including the use of coursed granite rubble, Caernarvon arches over doorways, and traces of external lime render on the north and east walls, date the castle to no earlier than the late thirteenth century. Now protected as National Monument No. 486 under state guardianship, Ballymoon Castle remains a compelling example of Anglo-Norman fortification in Ireland, its weathered walls still commanding the landscape much as they did seven centuries ago.