It measures roughly four metres east to west and three and a half metres north to south, sinking only about forty centimetres below the surrounding surface. That modest dip in the earth may be all that is visible of a souterrain, an underground stone-lined passage or chamber built during the early medieval period, typically used for storage, refuge, or both. The ground has settled and the outline has softened over the centuries, leaving only this faint geometric scar as a clue.

The depression sits in the north-western quadrant of the Kiltycahill rath, a ringfort whose own record is catalogued separately. Raths, the circular earthwork enclosures that dot the Irish countryside in their thousands, were the farmsteads of early medieval Ireland, and souterrains were a common feature within them. Their underground chambers were often carefully constructed from dry stone, designed to maintain a cool, stable temperature. The one at Kiltycahill has not been excavated, and the U-shaped depression at the surface is the only current evidence for what may lie beneath. Whether the structure below is intact, partially collapsed, or entirely infilled remains unknown.