A souterrain is an artificial underground structure, usually stone-lined or earth-cut, associated with early medieval settlement in Ireland, and thought to have served as storage space, a refuge, or both. The one at Bawnatemple gave itself away only because the ground gave way beneath farm machinery.

What the collapse revealed is a surprisingly intricate system for something sitting just 0.6 metres below the field surface. From the initial small oval chamber, cut into the earth rather than stone, narrow creepways, low connecting passages just wide enough to squeeze through on hands and knees, lead in several directions. One connects to a passage roughly two metres long, from which a tapering shaft extends upward, interpreted as an air-vent. At the far end of that passage, another creepway opens into the largest chamber in the system, an oval space about 3.5 metres across whose floor is cut directly into bedrock. Blocked-up construction shafts, the vertical openings used during building and then sealed afterwards, are visible at several points, with courses of stone still intact in the blocking. A small annexe off the main chamber was found filled with collapsed material. The whole structure sits within the south-western quadrant of what appears to be an early ecclesiastical enclosure, suggesting it was part of a monastic or church-associated settlement rather than a purely domestic site. A 1938 Ordnance Survey six-inch map also marks a second souterrain, likely stone-built, about 70 metres to the east, which indicates this part of Cork may once have supported a more substantial complex of underground works than the single accidental opening suggests.