The site at Belderny is a ringfort, the most common monument type in Ireland, yet this one carries a particular quiet oddity: the external fosse, the defensive ditch that once encircled the raised platform, has been interrupted along its northern, north-eastern, and south-western edges by large pits dug into it at some point after the original construction. The western arc of the fosse has disappeared entirely, leaving the enclosure's perimeter incomplete and somewhat ambiguous from ground level.

Ringforts were typically built between roughly the sixth and tenth centuries as enclosed farmsteads, the surrounding bank and ditch serving as much to define territory and signal status as to provide serious defence. Here, the platform is subcircular in plan, measuring around forty metres north to south and thirty-five metres east to west, defined by a scarp rather than a substantial upstanding bank. A causewayed entrance, where the ditch was left uncut to allow passage across it, may survive at the eastern side, suggesting something of the original approach is still preserved in the ground. What makes the interior additionally interesting is the presence of a souterrain, a stone-lined underground passage or chamber of the kind frequently found associated with ringforts across Ireland, typically interpreted as a place of storage or refuge. It is catalogued separately but occupies the same enclosed space, hinting at a domestic life that once animated this unremarkable corner of north Galway.