That quiet uncertainty is, in its own way, the whole point. A souterrain is an underground stone-built passage or chamber, typically associated with early medieval ringforts, thought to have served as storage space, refuge, or both. The one at Curraleigh has left no visible trace on the surface at all, and whether anything of it survives intact below ground remains unknown.

The sole record of its possible existence comes from P. J. Hartnett, who noted in 1939 what appeared to be a collapsed souterrain inside the rampart to the north-east of the enclosure. That careful hedge, "what appears to be", carries a lot of weight. Hartnett was observing surface evidence that has since disappeared entirely, leaving a site that is now essentially invisible twice over: the souterrain hidden beneath the ground, and its outward signs gone too. The ringfort it belongs to, a roughly circular earthwork of the kind that dots the Irish countryside in the thousands, still exists, but the subterranean feature it may once have contained is now a matter of record rather than observation.