A souterrain is an underground or semi-subterranean stone-built passage, typically associated with early medieval settlement in Ireland, often used for storage, refuge, or both. This one is set within an earthwork mound on a broadly sloping western hillside, and rather than running in a straight line, its passage zig-zags from the base of the mound up to its crest, climbing more than two metres in elevation between its western and eastern terminals.

The western end of the passage is where the structure is best preserved. The terminal wall is formed by a single upright slab, set into the lower outer scarp of the earthwork and resting on a foundation course of small stones. Just outside it, to the west, a large boulder sits in the ground, possibly placed there as a support stone. Moving inward, a 2.7-metre section of the passage survives intact, its side walls built three to four courses high from large stones and boulders, with corbels, slightly projecting stone ledges, at the tops of the walls. These corbels carry three massive limestone roof lintels, still in their original positions. The internal height at the southwest end of this section reaches 0.8 metres, though earthen infill toward the northeast end reduces the headroom to just 0.54 metres. Beyond this intact stretch, the story changes: the roof lintels are gone, and the rest of the passage survives only as a grassed-over depression roughly 2.4 metres wide and 0.4 metres deep, with stones showing through the turf. The full route of the passage runs level for 7.7 metres to the northeast, then turns south-southeast for 7.3 metres, before swinging east for a final 6 metres to reach the top of the mound, a total passage length of roughly 21 metres through a single earthwork.