This ancient structure once commanded views over the medieval harbour, though much of its early history remains shrouded in mystery. It may well be one of the three castles mentioned by Captain Venables when he described his assault on Carlingford in September 1649, a tumultuous period in Irish history when Cromwell’s forces swept through the country.

The building underwent significant transformation in the nineteenth century when the Coast Guard converted it for their use, cladding the entire interior with tongued and grooved timber and installing wooden stairs into the west wall. What survives today is a high vaulted ground floor measuring 7.2 metres east to west and 4.82 metres north to south, accessed through double doors facing the harbour. The rectangular structure, measuring 10.62 by 7.95 metres externally, features impressively thick walls ranging from 1.52 to 1.60 metres. The rounded vault soars to 4.3 metres at its centre, with the springing beginning 2.5 metres above the modern brick floor.

Archaeological investigation in 2008, when some of the Victorian timber cladding was removed, revealed fascinating medieval details. The north wall contains a double-splayed loop with a lintelled head, typical of defensive architecture, alongside a curious high-level cupboard with marks indicating it once had two small doors. The west wall tells a story of centuries of alterations; before the Coast Guard’s stairs, two large recesses existed here, one of which was later adapted to accommodate a stove pipe serving a ground floor stove. Behind the remaining timber cladding, traces of an older flue or doorway hint at the building’s complex evolution, whilst a blocked passage in the north side suggests internal routes through the thick medieval walls that are now lost to time.