It is a souterrain, an artificially constructed underground passage or chamber built in dry stone, typically associated with early medieval settlement in Ireland and thought to have served as a place of refuge, storage, or concealment. This one has partly fallen in, but a circular opening roughly a metre across once allowed a glimpse of corbelling inside, the technique by which successive courses of stone are stepped inward to form a rudimentary roof without mortar or formal arch.

The site occupies a particular kind of quiet valley, positioned towards the bottom of a north-facing slope in the drainage catchment of a small stream running south-east to north-west, close to that stream's source. The stream itself joins the River Lask about 750 metres to the north-west. The proximity to Kilnahue's parish church and its associated graveyard places the souterrain within a cluster of early ecclesiastical remains, a pattern that appears with some regularity across Ireland, where secular and religious occupation of the same ground accumulated over centuries, each layer eventually folding into the next.