Local tradition insists it exists, passed down through generations as quiet, persistent knowledge, but the precise location within the earthwork has been lost, and no living person can point to the spot.

A rath is a ringfort, typically a circular enclosure defined by an earthen bank and ditch, built and occupied during the early medieval period in Ireland, roughly between the fifth and twelfth centuries. They served as enclosed farmsteads, and many contain souterrains, underground stone-lined passages or chambers that were likely used for cool storage and possibly as places of refuge. The souterrain at Carrowreagh belongs, at least in tradition, to exactly this kind of site. What makes it unusual is not any particular feature of its construction, since nobody can describe that, but rather the way it survives only as memory. The rath itself is recorded, its presence confirmed; the souterrain beneath it exists in a stranger register, somewhere between archaeology and oral history, known but not locatable, believed in but unverified within living memory.