Set within the south-western quadrant of a ringfort, the subrectangular depression sits between the fort's inner bank and the traces of an old house site, and nobody is entirely certain what it once was. It may be the collapsed remains of a souterrain, an underground stone-lined passage or chamber typically built during the early medieval period as a place of storage, refuge, or both. Or it may be something more prosaic: a small quarry, suggested by a heap of upcast material piled at its south-eastern side.

The ambiguity is genuine rather than merely cautious. Souterrains are commonly found in association with ringforts, the circular earthwork enclosures that dot the Irish landscape in their thousands and date broadly to the first millennium AD. Their underground chambers were entered through narrow passages and could serve as cool stores for dairy produce or as places to shelter in times of danger. A collapsed example can look, from the surface, very much like a hollow left by the extraction of stone or soil, particularly when spoil has accumulated nearby. At Rathconrath, the ringfort itself occupies a slight rise with open views across much of the surrounding countryside, the sightlines interrupted only by higher ground to the south-east, south, and south-west. It is a position that would have made practical sense to whoever settled there, and the structures within it, whatever their precise function, reflect a carefully organised use of the enclosure's interior space.