It is easy to overlook, and that is rather the point. The hollow, orientated roughly northeast to southwest, is thought to be the collapsed or infilled trace of a souterrain, an underground stone-lined passage or chamber typically associated with early medieval settlement in Ireland. These subterranean structures were built to serve as storage spaces, places of refuge, or both, and their presence beneath a ringfort interior is not uncommon, though no two are quite alike.

The earthwork enclosing it is a rath, a circular enclosure defined here by two earthen banks with a fosse, or ditch, running between them. The rath measures roughly 27 metres in diameter, which places it at the smaller end of the scale for such sites. It survives in fair condition, though the fosse and outer bank are now legible only on the eastern and southwestern sides, the rest having been reduced over centuries of agricultural use. Raths of this type are generally dated to the early medieval period, roughly the fifth to twelfth centuries, and represent the enclosed farmsteads of the period's rural population. The possible souterrain sits in the southwestern quadrant of the interior, identifiable at ground level as little more than a depression, the rectangular outline hinting at deliberate construction beneath.

The site sits on a slight rise, which would have offered its original occupants both drainage and visibility across the surrounding landscape. What remains above ground is modest, a grass-covered earthen ring with a suggestive hollow at its heart, but the combination of a double-banked enclosure and a probable underground chamber gives Moneyveen a quiet complexity that rewards a careful look rather than a passing glance.