It is, in fact, the collapsed remains of a souterrain, an underground stone-lined passage typically associated with early medieval ringforts and used for storage or refuge. This one traces a shallow arc for approximately ten metres through the interior of the enclosure, running from the south-west perimeter toward the north-north-east. It is barely a metre wide and sinks only about forty centimetres into the earth, its edges marked by stones that protrude at odd angles through the grass.

The rath itself, recorded as MA062-128, is a ringfort, the kind of circular earthen enclosure that was once the standard unit of rural settlement in early medieval Ireland. Souterrains were commonly built within or beneath such enclosures, constructed from dry-stone walling and roofed with large flat lintels. Here, only one of those roof stones survives in place, sitting toward the north-north-east end of the passage. The rest of the structure has subsided over the centuries, leaving that characteristic grassed-over furrow. Much of what remains is further obscured by a dense growth of blackthorn scrub, which has colonised the depression and the surrounding area, making the full extent of the feature difficult to trace from ground level.