No hollow, no mound, no scatter of stone gives any indication that it is there. The structure is a souterrain, a type of man-made underground gallery built in early medieval Ireland, typically in drystone or rock-cut form and associated with nearby settlements, where they may have served as places of refuge, food storage, or concealment. This particular example was known to no one until 1982, when building operations cut through the ground and exposed it.

The souterrain is L-shaped in plan and constructed entirely in drystone, meaning the walls and roof lintels are assembled without mortar, relying on the careful placement of stone alone. Three chambers are connected by two narrow passage sections known as drop-hole creeps, a distinctive feature in which a person must drop down through a constricted opening to move from one chamber to the next. The first chamber, running roughly south-south-east to north-north-west and measuring 6.5 metres long, was entered at its northern end where roof lintels had already collapsed. A creep just two metres long and no more than seventy centimetres wide leads off its north-north-east side into the second chamber, which is slightly taller at 1.8 metres and runs east-north-east to west-south-west. A second creep at the far end of that chamber, lower and tighter than the first, opens into the third and final chamber, which is four metres long and similarly aligned. The structure was surveyed by Buckley and O'Brien in 1985 and 1986, giving researchers their only real record of what lies below the field.