It is a small fort, compact and wind-scoured, and the landscape around it tells several stories at once: the pasture and sand dunes are laced with lazybeds, the raised cultivation ridges that mark centuries of subsistence farming, and the headland itself sits forty feet above the water, commanding views in several directions while remaining visible from the surrounding land.

A promontory fort uses the natural geography of a headland as its primary defence, cutting off the landward approach with a bank and ditch rather than enclosing the entire perimeter. At An Teanach, that barrier is a single earthen and stone bank, roughly 4.5 metres wide with a slightly convex face towards the land, behind which lies a U-shaped ditch eight to ten metres wide at the base. The ditch, known as a fosse, averages around 1.5 metres deep, and several large stone slabs along its inner face may be the remnants of revetting, the structural lining used to stabilise an earthen cut. A subtle rise in the floor of the fosse near the western end may mark where an entrance causeway once crossed. The interior, measuring 25 metres by 21 metres, is nearly level and largely featureless apart from old cultivation ridges. What gives the site particular interest is a section exposed by recent cliff slippage along the western edge, which has peeled back the surface to reveal the old ground level 0.35 metres below, along with the vertical slab revetting of the original bank. It is the kind of accidental archaeology that coastal erosion occasionally delivers. The site was documented as part of Markus Casey's 1999 survey of coastal promontory forts across Sligo, Mayo, Galway and Clare, and a larger defended headland lies immediately to the east, suggesting this stretch of coastline was once considered worth holding in some deliberate and organised way.