A souterrain, as these man-made underground passages are known, is typically an early medieval construction, built from stone and used for storage, refuge, or both. This one had not been entered through its original doorway; the collapse of the roof of its main chamber was what finally let daylight in.

The structure, recorded by Ryan in 1975, is more complex than a single tunnel. The central feature is a subrectangular beehive chamber, roughly 2.9 metres by 2.64 metres, from which a lintelled passage, no more than 0.94 metres wide and varying between half a metre and just over a metre in height, extends eastward for about three metres. At its eastern end the passage opens slightly into a small chamber roofed by two large flat stones, then turns south into a less regular passage running nearly 3.4 metres before turning west and meeting a complete blockage. Ryan noted that the original entrance was likely close to that blocked western end, though it has not been identified. The whole arrangement, with its deliberate turns and constrictions, is characteristic of souterrains designed to make movement difficult for anyone unfamiliar with the layout, a feature thought to have defensive as well as practical value.

The site sits on sloping ground, and the subsidence that revealed it serves as a reminder that many such structures across Ireland remain undetected beneath farmland, their roofstones quietly shifting under the weight of centuries.