What occupies it is a promontory fort, a type of coastal enclosure found around Ireland's seaboard in which earthen banks and ditches were thrown across the neck of a headland to create a defended space, with the cliffs doing the rest of the work. At An Bheithigh, three such banks and two intervening ditches survive, though barely. The banks average just 0.35 metres above ground level and are partly smothered in vegetation, leaving a site that rewards close attention rather than a casual glance.

The fort is modest in its dimensions, 35 metres long by 18 metres wide, and time has not been kind to it. The inner face of the innermost bank has been worn down to a scarp, and the full stretch of defences now runs to only seven metres. A natural cleft, 1.5 metres deep, 30 metres long, and about a metre wide, cuts along the northwestern edge of the headland, suggesting the builders were working with the landscape as much as reshaping it. A modern path crosses the northeastern cliff edge by way of an artificial causeway, which is thought to be the only surviving indication of where an original entrance once stood. Some undulations to the southeast may represent further earthworks, and a possible hut-site has been noted near the path, though neither feature is clearly legible on the ground. What makes the site additionally curious is its near-total absence from the documentary record: it was not included by the antiquarian Thomas Johnson Westropp in his catalogue of Irish promontory forts, and it does not appear on any of the Ordnance Survey maps. It was brought to wider attention through a 1999 survey conducted by Markus Casey as part of an MA thesis examining coastal promontory forts across counties Sligo, Mayo, Galway, and Clare.

The coastline itself offers a clue to the fort's present condition. The narrowest point of the headland's neck now lies six metres outside the line of the defences, which suggests the cliffline has retreated through erosion since the fortifications were first constructed. The banks that once guarded a wider approach have, in effect, been left slightly adrift, with the sea gradually reclaiming the ground between them and the edge.