A souterrain is an underground stone-built structure, typically associated with early medieval settlement in Ireland, used for storage, refuge, or both. That the builders of this one incorporated pieces of broken millstones into the fabric of the walls rather than discarding them tells a quiet story about economy and practicality in early rural life.

The structure itself is carefully made. Its entrance, just over a metre wide, opens in the north-west face of a quarry and leads into a stone-lined passage running north-east to south-west, roughly four metres long and tall enough to stand in comfortably. At its far end, the passage slopes downward and narrows sharply into a creepway, a low constriction less than seventy centimetres high, through which a person would have to squeeze on hands and knees. Beyond this bottleneck opens a beehive-shaped chamber, corbelled in the traditional Irish manner with stones projecting inward course by course, and sealed at the top by a single large capstone. The chamber measures nearly two and a half metres across and the same height, a surprisingly generous space given the effort required to enter it. The site was first recorded by Courtenay Moore in 1900, at the time on land belonging to a Mr Rialli, and was examined again by J.C. Coleman in 1947. A second souterrain of similar construction lies close by, suggesting this area once supported a more substantial settlement than the quiet knoll now implies.