Known locally as Cromwell's Head, it is worn enough that the facial features are largely indistinct, though it appears to wear some kind of head covering and has a ribbed neck. Whether the carving predates the present building by centuries or arrived with it is unclear, but it is the kind of detail that lodges in the mind long after the architecture itself has faded.

The house at Castlekevin is a castellated country house, meaning it was built in the Gothic Revival manner with battlements, towers, and the general silhouette of a medieval fortress, though without any genuine defensive function. The south-facing entrance front presents a central block flanked by four-storey semicircular towers complete with fake machicolations, the projecting corbelled galleries that in a real castle allowed defenders to drop objects on attackers below. An ashlar limestone porch with corner turrets completes the theatrical effect. According to Samuel Lewis writing in 1837, the house was rebuilt around that period by one E. Badham Thornhill, to a design by an architect named Flood. But the site is considerably older. A castle is recorded here on the Down Survey barony map of 1655 to 1656, and a datestone on the parapet wall carries the inscription "1613/T/W/I", placing something substantial here well before the present building. Some of the internal dividing walls run to around a metre in thickness, suggesting that Flood's design absorbed rather than replaced what was already standing. A partially blocked pointed doorway in the field wall to the west bears a keystone dated 1831, a quiet footnote to the building campaign.

The blocked upper windows on both the east and west elevations give the house an oddly shuttered quality from certain angles, as though parts of it have been deliberately turned inward. Farm buildings survive to the northeast, and the irregular fenestration of the rear elevation, with its five-sided projecting bay, suggests a building that accumulated compromises over time rather than arriving fully resolved.