What lies beneath, or what once lay beneath, is a souterrain, an artificially constructed underground passage or chamber built of dry stone, common in early medieval Ireland and typically associated with nearby settlement sites. This one was known locally by the name Sálín Crú, rendered phonetically as Sawleen Crew, a name that survived in local memory and was recorded in the topographical files of the National Museum of Ireland, even as the structure itself quietly disappeared from view.

When Neary examined the site in 1914, the entrance chamber was still partly accessible. It was lined with loose-stone masonry and roofed with heavy flagstones, measuring roughly 1.5 metres wide, 2.75 metres long, and 1.5 metres high. Neary noted that it had once been considerably deeper, and that a passage ran eastward from it at a depth of around five feet, though by that point the passage had been choked with sand, the work of burrowing rabbits. By the time the site was marked on the third edition of the Ordnance Survey six-inch map in 1930, it was already recorded as isolated, meaning no associated settlement features were mapped alongside it. That said, two ringforts, the circular earthwork enclosures most commonly linked with early medieval farming settlement, lie within 375 metres to the east and south-east, hinting at the kind of agricultural landscape in which souterrains typically appear. Whether this one served as a place of refuge, a cool-store for dairy produce, or something else remains, as with so many of its kind, an open question.