The structure in question is a souterrain, an underground passage or chamber built by early medieval communities, typically for storage, refuge, or both, and its disappearance from view is itself a small archaeological puzzle.

The souterrain sits inside a rath, a circular earthen enclosure of the kind built across Ireland from roughly the early Christian period onward, often serving as a farmstead boundary. Local knowledge had long held that a stone-lined hole existed at the northern end of this particular rath, and it was apparently still visible to observers in the mid-twentieth century. By the time the site was formally inspected in 1995, however, no clear trace of it could be found. What the inspection did turn up was a shallow linear depression, around four metres long and just under one and a half metres wide, with a low raised lip along its western edge, positioned at the highest point of the interior ground in the north-west of the enclosure. Whether this depression is a collapsed remnant of that earlier feature, or something coincidental, remains unresolved. Adding a further layer of interest, a second souterrain, this one unenclosed, sits roughly fifty metres to the north of the rath, suggesting that the immediate landscape around Corimla once held more underground architecture than is now easy to read from the surface.