Built between 1235 and 1240 by Meiler de Bermingham, this rectangular keep forms part of a larger D-shaped bawn whose walls also served as part of the town’s defences. The castle’s random-rubble construction with dressed quoin stones and pronounced base batter speaks to the military architecture of its time, whilst its three-storey height with gabled attic represents centuries of modifications and improvements.

The original two-storey structure reveals the dual nature of medieval castle life; both fortress and residence. The first floor served as the public hall, accessed through an ornate pointed arch doorway reached by external steps, with decorated capitals on the doorway columns and window embrasures showcasing the wealth and status of its owners. Four tall windows, one centrally placed in each wall within deeply splayed embrasures, flooded the space with light. The ground floor, originally reached by internal wooden stairs or ladder, likely served as storage with its four small windows providing minimal illumination. A garderobe chamber projecting from the north corner, complete with narrow slit windows and an external cesspit excavated in 1989, provided the medieval equivalent of indoor plumbing.

The castle underwent significant changes around 1250 when the walls and roof were raised and a gallery added to the southwest end, evidenced by masonry arch remains and beam holes still visible today. The 15th century brought further alterations including high gable ends, a vaulted ground floor supported by three central pillars and side walls, and a new ground-floor doorway. The crenellated parapet with its cruciform arrow loops and evidence of hoarding defences remind visitors of the castle’s military purpose. Following 1990s restoration by the Office of Public Works, the building now houses an audio-visual theatre on the second floor, with wooden floors throughout and a steel stairway installed in 2018 replacing earlier wooden access to the first-floor entrance.