It is almost the only outward sign of a souterrain beneath, an artificial underground passage built in early medieval Ireland, typically for storage or refuge, constructed here from drystone masonry and roofed with a series of large flat slabs. The passage extends at least three metres to the north-north-west, but it has silted and collapsed to within a quarter of a metre of its own roof, leaving it entirely inaccessible. Only that one exposed lintel marks its presence.

What makes this site quietly puzzling is the absence of any tradition linking it to a known monument above ground. Souterrains are commonly found in association with ringforts, the circular enclosures, usually defined by an earthen bank and ditch, that served as defended farmsteads throughout early medieval Ireland. Here, seven ringforts have been recorded within six hundred metres of the site, and yet none is formally connected to the souterrain. Whether it originally served one of those nearby enclosures, or belonged to some structure that has since vanished entirely from the landscape, is not recorded. The passage itself, just 0.7 metres wide at roof level, is modest even by the standards of its type, suggesting a functional rather than elaborate construction.