The castle’s strategic position made excellent use of natural defences; cliffs protect it on the north, west, south and southeast sides, whilst steep slopes guard the east and northeast approaches. Today, only the southwest corner survives to a height of two storeys, built from rubble construction with coarse sea-sand mortar. The missing quoin stones, once made of dressed ashlar, have left behind tell-tale bond holes that hint at the structure’s former appearance.

The castle’s documented history reveals a succession of occupants and gradual decline. In 1601, Alexander McDonaloghe inhabited the tower house, but by 1610 it had been granted to Henry Vaughan. A 1622 report paints a picture of decay and makeshift repairs, describing how Arthur Terry, Vaughan’s assignee, had attempted to make the structure habitable by adding a thatched roof of birch timber to what was already “an old Irish castle” with partially repaired walls. Terry also constructed a modest stone court adjoining the castle, standing just five feet high and built without clay or lime mortar. By this time, however, Terry had abandoned the site for Londonderry, leaving the castle waste. The Civil Survey of 1654-6 would later dismiss it as merely “the little old pile of stone called Moyross Castle”.

The surviving architecture reveals fascinating defensive features typical of Irish tower houses. A mural passage runs through the ground floor of the west wall, measuring about 1.4 metres high, with what appears to be a rebated door jamb at the north end. The first floor shows evidence of a murder hole shaft; a defensive feature that would have allowed defenders to attack intruders from above. Windows were deeply splayed for defence, with one surviving example in a sub-rectangular embrasure at the north end of the west wall. Stone facing was added to reinforce the cliff face on the north side, likely to support the northwest corner of the tower. The area south of the tower house may have once been enclosed by a bawn wall, and this could be where the house mentioned in the 1622 report once stood.