A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval ringforts and thought to have served as storage space, a refuge, or both. At this particular site, there is no visible surface trace of it whatsoever, which puts it in an unusual category: a structure that is known, recorded, and named, but effectively invisible.

The sole historical thread connecting anyone to this feature comes from P. J. Hartnett, who noted in 1939 that a local source had told him of "a cave near the entrance" to the ringfort, the circular enclosed settlement within which the souterrain is believed to lie. That secondhand account, passed on over eighty years ago, is essentially all there is. No excavation appears to have confirmed the structure's dimensions, construction, or condition. It sits in the record as a place-memory more than a documented monument, the kind of detail that survives precisely because someone once thought to write it down.