A machine widening the apparent cavity broke through into a barrel-vaulted earth-cut chamber, the kind of underground structure known as a souterrain, a type of man-made underground passage or chamber built during the early medieval period in Ireland, typically associated with nearby ringforts and used for storage, refuge, or both.

The chamber itself is modest in scale, ranging between 1.35 metres and 2 metres in width east to west, and running approximately 3.5 metres north to south. Steps or ledges appear at both the south and north ends, with evidence of stone-facing surviving at the south-west. The north end leads into a shallow splayed recess blocked with drystone walling, which archaeologists from Tobar Archaeological Services suggested might represent a construction shaft that was later backfilled or deliberately sealed, though this remained unconfirmed at the time of the initial inspection. A shallow recess in the east wall adds further complexity to the layout. Most intriguingly, directly opposite that recess, a narrow creep, which is the term used for a low connecting passage between souterrain chambers, extends out in a north-westerly direction. At only around 0.6 metres wide at its opening and apparently narrowing further, it could not be safely explored during the first visit. Stones visible along the creep suggest the passage turns north or north-east, and there may be a second chamber beyond, though that too remained unverified when the site was first recorded by Miriam Carroll of Tobar Archaeological Services in April 2015.