It is a souterrain, a type of stone-lined underground structure built during the early medieval period in Ireland, typically associated with ringforts and used for storage, refuge, or both. What makes this particular example worth pausing over is how well it has survived, and how precisely its geometry can still be traced.

The structure is drystone-built, meaning its walls are constructed from carefully fitted stone without the use of mortar, and it follows a roughly T-shaped plan. The first chamber, running east to west, measures 7.75 metres long and 1.75 metres wide, with its entrance opening at the eastern end. About five metres in from that entrance, a creep connects off the southern wall. A creep is a deliberately low and narrow passage, just 1.47 metres long and 0.86 metres wide in this case, designed to slow or obstruct anyone trying to force their way through. Beyond it lies a second chamber, oriented north to south at a right angle to the first, running to 6.4 metres in length and up to 1.73 metres wide at its broadest point. The deliberate awkwardness of the creep, combined with the change of direction between chambers, points to a structure designed as much for security as for storage. Anyone unfamiliar with the layout would have found themselves disoriented underground, which was rather the point.