The site has no visible surface trace, which places it in a quietly peculiar category: archaeologically recorded, locally remembered, and effectively invisible.

A souterrain is a man-made underground passage or chamber, typically stone-lined and associated with early medieval settlement. They were built beneath or beside ringforts, the circular enclosed farmsteads that dot the Irish countryside, and were used variously for storage, refuge, or both. At Ballynatona, the souterrain sits within a ringfort, and what little is known about it comes from two sources: a note made by a researcher named Broker in 1937, who recorded simply an "underground chamber", and local information passed down over the years describing it as stone-lined. Neither source is especially detailed, and nothing visible now confirms either account. The structure, if it survives intact underground, has left no depression, no collapse, no exposed masonry at the surface to betray its presence.