A cashel is a stone-walled circular enclosure, typically of early medieval date, used to protect a farmstead or settlement, and within the north-western quadrant of this one, three shallow depressions have been observed in the surface, largely filled in with loose field stones. They may represent nothing more than subsidence and accumulated rubble. Or they may mark the line of a collapsed souterrain, the kind of underground stone-lined passage or chamber that was commonly built beneath and beside early Irish settlements, serving as storage spaces, refuges, or both.

The clearest piece of evidence for a souterrain here came not from the surface depressions but from a brief exposure recorded in 1979. During clearance works near the outer slope of the cashel wall on the south-east side, a short length of a lintelled stone passage came to light, measuring roughly half a metre wide and a quarter of a metre high. Whether this was a drainage channel or a souterrain vent, a subsidiary passage designed to introduce air into a larger underground system, could not be confirmed at the time. By 1999, when the site was inspected again, the feature had disappeared back into the ground, either reburied or obscured, leaving only the written record of what had briefly been visible.