A souterrain, to use the archaeological term, is a man-made underground structure, typically drystone-built, associated with early medieval ringforts and cashels across Ireland. They were used variously for storage, refuge, or both, and their low, narrow entry passages were likely a deliberate defensive feature. This one is particularly well-preserved.

The structure consists of two connected sections: a creep and a chamber. The creep is the entry passage, a tight crawlway roughly two metres long, just under a metre wide, and only forty centimetres high, meaning anyone entering would have had to press themselves almost flat to the ground. It opens into a rectangular chamber running roughly north-northeast to south-southwest, nearly six metres long and reaching a maximum height of around one and a third metres, still not enough to stand upright. The floor is a mix of clay and small stones, but roughly halfway along, a natural rock ledge raises the floor level by about forty centimetres, and the builders accommodated this by raising the roofline at the same point, a small but telling piece of practical craftsmanship. The total length of the structure exceeds seven and a half metres. A possible side stone to the north-northwest of the creep, aligned to the south-southwest, may point to the existence of a second chamber that has yet to be fully confirmed.