That uncertainty is, in itself, the most interesting thing about this site. A souterrain is an underground stone-lined passage or chamber, typically constructed during the early medieval period in Ireland and often associated with nearby settlement sites, used variously for storage, refuge, or purposes we still debate. At Rossacoosane, local tradition insists one exists, but the surface of the land gives nothing away.

The reputed souterrain appears in the archaeological survey of the Iveragh Peninsula compiled by A. O'Sullivan and J. Sheehan, published by Cork University Press in 1996. The survey records the local reputation plainly and without embellishment, noting that no surface trace of the feature is evident. It is a small, honest entry: a community's collective memory of something underground, set against the silence of the soil above it. Whether the structure was backfilled, collapsed inward, or simply never existed in the form tradition describes, the record does not say.