This roughly D-shaped fortress, measuring about 30 metres across, uses the natural cliff edge as its defensive boundary to the northwest whilst a curtain wall completes the enclosure from northeast to southwest. Though now overgrown with thorns, briars and ivy, the castle’s curtain wall survives in five straight sections of varying heights and thicknesses, punctuated by the fragmentary remains of two towers; one at the southern corner projecting outward from the wall, and another collapsed tower at the eastern corner projecting inward.

The castle’s entrance gateway, located along the eastern stretch of the curtain wall, features a pointed arch of rough voussoirs and remnants of a drawbar socket, though it’s now buried to more than half its height in rubble. Inside the curtain wall, a sophisticated defensive system once operated through a mural stairway that rose through the wall itself, connecting to the first floor chamber of the south tower and continuing along a roofed passageway atop the fortification. The south tower, whilst largely reduced to a hawthorn covered mound, still shows evidence of its former two storey height in its surviving north wall, complete with the broken remains of a first floor doorway and traces of vaulting springs.

As the ancestral seat of the O’Sullivan Beare tanist, Ardea Castle witnessed significant historical events, including a Spanish landing of money and ammunition in 1601 during the Nine Years’ War. Local tradition holds that Cromwellian forces sacked the castle in the 1650s, which would explain the particularly violent destruction of the south tower, where massive chunks of bonded masonry lie scattered far down the slope below, apparently blown from their original positions. Within the castle grounds, the foundations of a rectangular structure and a curious sunken feature near the cliff edge hint at the domestic life that once filled this now silent fortress, which has stood in its current ruined state since at least the 1840s.