It does not announce itself with any surface trace, and nothing marks its presence from above. It came to light only by accident, in April 1960, when a plough broke into it.

A souterrain is a drystone-built underground passage or chamber, constructed without mortar, typically associated with early medieval settlement in Ireland and thought to have served for storage, refuge, or both. The one at Sandfordscourt was recorded at the time of its discovery from an Office of Public Works topographic file, which preserves a description worth quoting at length: thick flagstones were laid on top of one another to form a flat vertical face on the inside, while the outer face was rougher and less regular, the wall being a single course of stones throughout. The capstones sat edge to edge, resting directly on the walls without projecting much beyond them. The open end of the trench was rounded, shaped by stone lining that was described as not very carefully done, and the far end appeared to terminate in a similar fashion. The structure sits on the valley floor in wet pasture, with open views across the valley in all directions, which may suggest proximity to an early settlement or farmstead whose other traces have long since vanished. After its discovery, it seems the intention was to fill the feature back in with stones and clay, which would explain why nothing remains visible at ground level today.