The evidence is local tradition, a memory of stone flags turned up at some point in the interior of the fort, and a shallow, roughly circular depression in the ground, two to three metres across, sitting to the east of centre. That depression is the most tangible clue available, and it amounts to little more than a dip in the earth.

A souterrain is an underground stone-lined passage or chamber, built during the early medieval period, typically as a place of refuge, cold storage, or both. They are usually entered through a narrow opening and roofed with large flat slabs, the kind of lintel construction that the remembered stone flags would fit neatly into. The ringfort in which this one supposedly lies is a separate, catalogued monument in its own right, a circular enclosed settlement of the sort that dots the Irish countryside in the thousands, most of them dating from roughly the sixth to the twelfth centuries. Whether the souterrain was constructed as part of the same occupation of the site is unknown. What local tradition preserved is only the fact of the flags, not when they appeared, who found them, or what became of them. The precise location within the fort remains uncertain, and the surface depression, suggestive as it is, has not been excavated to confirm what lies beneath.