It is easy to miss from the surface, but what it marks is the roofline of a souterrain, an underground stone-lined passage built by early medieval farmers, typically used for storage, shelter, or refuge. This particular example extends eight metres before a branch turns southward for a further three, giving it the modest but purposeful L-shaped character common to the type.

Souterrains are almost always found in association with ringforts, the circular enclosed settlements that were the standard form of rural habitation in Ireland from roughly the seventh to the twelfth centuries. The ringfort here, recorded separately, still retains its bank, though it has been broken through to the south-east, and it is at that breach where the souterrain's trench becomes visible. The passage itself is about 0.8 metres in depth at the point of entry, which gives some sense of how close to the surface its upper course runs. Whether the original stone lining survives intact beneath is not recorded, but the earthwork trace alone is enough to confirm that something deliberate and organised lies underground.