This is a souterrain, an underground stone-lined tunnel constructed in early medieval Ireland, typically by drystone walling and capped with large flat roofing stones called lintels. Their precise purpose is still debated, but they are generally understood to have served as places of refuge, storage, or concealment, built by farming communities for whom a concealed underground chamber was a practical asset.

This particular souterrain has two openings at surface level. The first, in the south-western part of the site, is just over a metre wide and half a metre high, leading into a lintelled passage that runs north-westward for roughly five metres, rising to a more comfortable internal height of around 1.3 metres. The north-western end of this passage has partially collapsed. A second opening lies to the north of the first and was not originally designed as an entrance at all; it came about when one of the roofing lintels gave way, breaking open a separate passageway aligned north to south. The result is a structure with two points of entry, one intentional and one accidental, which together offer a sense of how the underground space was arranged across the western portion of the site. The construction, drystone throughout, places it within a tradition of early medieval craft found across Ireland, where builders shaped chambers and corridors from uncut stone without mortar, relying entirely on the precision of placement and the weight of earth above to hold everything in place.