Local tradition holds that a souterrain runs under the earthwork, yet there is no visible trace of it on the surface, no tell-tale depression, no collapsed lintel, no darkened hollow in the grass. It exists, if it exists at all, entirely as memory.

Souterrains are underground stone-lined passages or chambers, typically associated with early medieval ringforts in Ireland, and thought to have served as places of refuge, cold storage, or concealed escape routes. The ringfort at Lisrobin is a known archaeological site, and the pairing of a ringfort with a souterrain is not unusual in Cork or elsewhere in the country. What is unusual here is the complete absence of physical evidence. The tradition of a tunnel survives in local knowledge, passed along without the confirmation of stonework or excavation, which puts it in a curious category, neither confirmed nor dismissed, simply waiting.