Known as An Dún, the fort is positioned not for convenience but for maximum exposure, perched where the mountain drops away sharply into the Atlantic. The result is a structure whose builders trusted the sea to do some of the defensive work for them, leaving only the landward sides to be protected by earthworks and stone. What survives is heavily ruined and difficult to read, but the underlying logic of the design remains legible in the landscape.

The two platforms are separated from each other and from the surrounding hillside by a fosse, a cut defensive ditch, which runs around most of their perimeters before the cliff-face takes over to the north-west. The sides of these raised platforms were once revetted with drystone walling, possibly built in two tiers, though most of this has long since collapsed into the fosse below. An earthen outer bank, averaging around 6.5 metres wide and rising up to 2 metres, sits beyond the fosse on the landward side. A narrow break on the south-east side of the western enclosure is the most plausible candidate for an original entrance, partly because a corresponding, if indistinct, gap appears in the inner defence as well. The western platform, measuring 13 metres by 7 metres, once contained two large clocháns, the corbelled dry-stone huts associated with early Irish settlement, recorded by Mason in 1950 though now largely reduced to stony banks and collapse. The eastern platform is considerably larger at roughly 19 metres by 14 metres, and near its centre lies a partly drystone-lined depression that may represent a souterrain, an underground passage or storage chamber, though this interpretation remains uncertain. A trackway running up from the village at the north-east end of the island passes immediately outside the outer bank; it was most likely built to carry turf down from the mountain, and its proximity to the fort is probably coincidental rather than connected to the site's original use.

The island is accessible by ferry from Dunquin on the Dingle Peninsula, and the fort lies some distance uphill from the village, reached by following the old turf trackway towards the summit ridge. The site itself gives little away at first glance; the collapse is extensive, and what reads as deliberate architecture requires some patience to distinguish from the general scatter of stone across the slope. The cliff-edge along the northern perimeter is real and close, and the low stony banks that mark the platform edges continue right up to the drop.