A shallow linear depression in the south-western quadrant of a rath at Lisgormin runs for just over ten metres towards the north-east, measuring roughly 3.6 metres wide but barely 0.2 metres deep. Stones protrude from the sod at its south-western end, hinting at underlying structure. Whether it is a natural feature, a collapsed ditch, or something more deliberate remains genuinely unresolved.

The tentative identification here is that of a souterrain, an underground stone-lined passage or chamber typically associated with early medieval ringforts across Ireland. Souterrains were built for various purposes, most commonly storage or refuge, and their entrances were often concealed within the interior of a rath, the circular earthwork enclosure that served as a defended farmstead. At Lisgormin, the depression sits within the rath's interior, extending inward from the scarp, which is the steep inner face of the surrounding bank. Stones visible at the surface suggest that something was once built here, but the feature is so slight and so thoroughly grassed over that its true character cannot be confirmed without excavation. Its significance, as the record plainly acknowledges, remains unclear.