The structure is a souterrain, a type of man-made underground passage or chamber system built during the early medieval period in Ireland, typically used for storage, refuge, or a combination of both. What makes this particular example quietly compelling is the precision with which it was engineered into the earth, and the fact that it lay undiscovered until 1987, when the ground gave up its secret after perhaps a thousand years of concealment.

The souterrain consists of three earth-cut chambers connected by creepways, the narrow low passages that force anyone moving between chambers to crawl, which would have made defence or simple security considerably easier. The first chamber is subrectangular, roughly 2.88 metres long and 1.35 metres wide, with a pointed roof and its long axis running north to south. A creepway in the west wall leads into the second chamber, which is roughly oval in plan, slightly shorter at 2.3 metres, with a rounded roof and its own creepway continuing the sequence into a third chamber. That third chamber, also oval and the smallest of the three at around 2 metres in length, has a domed roof that has partially collapsed at its centre. The original entrance, now collapsed, was at its northern end, and the floor is covered in spoil from that collapse. Each chamber also retains an infilled construction shaft, the vertical cuts made from the surface during building to allow workers to excavate the chambers from above, then sealed once the structure was complete. These shafts are a useful reminder that souterrains, for all their subterranean atmosphere, were carefully planned constructions rather than natural formations.