This is a souterrain, an artificial underground passage or chamber built during the early medieval period, typically by the same farming communities that constructed the circular enclosed settlements we call ringforts. Where a souterrain survives intact, it appears as a stone-lined tunnel, sometimes corbelled overhead, used most likely for food storage and possibly as a refuge. At Moneyveen, the structure is no longer intact in that sense; what remains visible is the depression left behind after the roof gave way, tracing the shape of the original passage in the earth itself.

The hollow runs on a north-south axis for most of its length before turning sharply westward at its northern end, continuing briefly on an east-west line. That right-angle bend is characteristic of souterrain design across Ireland, where changes in direction were sometimes used to control airflow, to slow the movement of smoke, or simply to make the interior less navigable to anyone forcing entry. The parent ringfort, a class of monument that dates broadly to the early medieval period between roughly the sixth and twelfth centuries, still surrounds the feature, placing the souterrain in the south-west quadrant of the enclosure. The two would originally have functioned together as parts of the same farmstead complex.