Whilst the site lacks detailed historical records, it does appear on a Down Survey map from 1655-6, and we know the land belonged to one Francis Bryver of Waterford in 1640. The rectangular tower, measuring 9.7 metres north to south and 8.7 metres east to west, features a subtle base batter and cut-stone quoins, though today only its ground floor remains fully intact.

The tower’s ground floor reveals the practical design typical of Irish tower houses. A now-destroyed doorway once stood near the northern end of the eastern wall, originally protected by a guardroom built into the northern wall. This entrance led through a lobby into the main ground-floor chamber, a space measuring 6.2 by 4.75 metres internally. The chamber featured round-headed windows in the north, west and south walls, whilst a destroyed fireplace occupied the southern wall. For the comfort of its medieval inhabitants, a garderobe with a corner loop was built into the northwest angle. Mural stairs within the eastern wall provided access to the first floor, which was supported by corbels projecting from the east and west walls.

Evidence from the first floor suggests a well-appointed living space, with corner loops at the southeast and southwest angles providing both light and defensive capabilities. A window pierced the southern wall, whilst another garderobe was positioned in the northern wall for convenience. Though no vaulting survives, the first floor may have functioned as a loft beneath a north-south vault. The remnants of stairs rising eastward from the centre of the northern wall at first-floor level hint at additional upper storeys, now lost to time. Archaeological testing conducted in 2006 in a nearby farmyard, approximately 35 metres south-southeast of the tower, yielded no materials related to the castle, leaving many questions about daily life at Cullen Castle unanswered.