This is a souterrain, an underground passage or chamber type common in early medieval Ireland, typically associated with ringforts and thought to have served for storage, refuge, or both. What makes this particular example worth attention is its geometry: four rectangular galleries, each running at a right angle to the next, roofed by large capstones and connected by low doorways flanked by upright stones called orthostats. The first gallery runs roughly north to south and measures about four metres in length, under a metre wide and just over a metre high; the others are of similar proportions. One small detail lodged itself in later investigations: a scatter of stone chips on the floor of the galleries, which the archaeologist J.P. McCarthy proposed in 1977 may not be debris at all, but an original feature of the construction.

McCarthy's investigation in 1977 was not the first serious look at the structure, and it was not the last. Power examined it again in 1985. Between them, the two investigations left a mound of spoil on the western side of the access point, a physical trace that McCarthy himself recorded. A construction shaft, the kind of opening cut from above during building to allow workers to manoeuvre stone into position, remains partly visible inside the second gallery. The doorway connecting galleries three and four differs slightly from the others: here the orthostats carry a lintel set just below the capstone rather than supporting the capstone directly, a small variation in technique that is easy to miss but speaks to the decisions made by whoever built this place. An opening at the western end of the fourth gallery may be the result of later collapse rather than an intended feature.

Access to the souterrain is still possible through a deep hole inside the ringfort bank, though the passage dimensions, roughly a metre high and less than a metre wide throughout, make clear that any visit requires a willingness to move on hands and knees through tight stone-lined spaces. The spoil mound to the west of the entrance hole marks where earlier investigators removed material and is itself now part of the site's visible history.