This four-storey rectangular structure, built from uncoursed rubble with remnants of interior plaster still visible, formed an integral part of the medieval borough of Newcastle. While its core dates to medieval times, the building underwent significant alterations in later centuries, creating a fascinating architectural palimpsest that reveals different periods of Irish history.

The castle’s western façade immediately catches the eye with three mysterious niches above the entrance, their concave limestone frames likely once holding armorial plaques that proclaimed the status of the castle’s occupants. Step through the entrance and you’ll find yourself in a barrel-vaulted chamber running east to west, with doorways on either side featuring chamfered granite portals and arches that lead to narrower vaulted chambers. A smaller chamber extends from the northeast corner, which appears to have been largely underground; perhaps it served as storage or even a holding cell. From the main ground floor chamber, a narrow stairwell built into the north wall leads to an intermediate room between the ground and first floors, complete with a large fireplace and, intriguingly, a window opening with a floor-level chute below; possibly for disposing of waste or receiving supplies.

The first floor’s main chamber, measuring six metres east to west and five and a half metres north to south, sits directly above the entrance vault and would have served as the principal living space. Two opposing windows in the east and west walls provided light and ventilation, whilst a brick fireplace in the southeast corner offered warmth. Though the original partition between this and the intermediate room has long since disappeared, along with the medieval means of access between floors, doorways and niches tell of additional chambers to the south. The niches positioned just above window level once supported the floor joists of the second storey, where yet another division created separate rooms. What remains today is a testament to medieval engineering and the continuous occupation and modification of this strategic stronghold through the centuries.