What collapsed into view was a souterrain, an artificial underground structure of the early medieval period in Ireland, typically cut from earth or built from stone and used for storage, refuge, or both. This particular example had been dug directly from the earth rather than lined with masonry, which makes it relatively unusual and also, as it turned out, structurally precarious.

The collapse exposed a main chamber roughly 3.5 metres east to west and 2.5 metres north to south, from which two narrow passages, known as creepways, led off about 1.2 metres apart into separate inner chambers. Creepways are exactly what the name suggests, low connecting tunnels that force anyone moving through them into a crawl, a feature thought to slow down or deter unwanted intruders. The westerly of the two inner chambers has a rounded roof and slopes gently downward to the south-west; the easterly one, slightly taller at 1.5 metres, has an A-shaped roof profile. Both chambers are partially filled with collapsed earth, and both show walls that appear smoke-blackened, suggesting they were used over a period of time and that fire or burning of some kind occurred inside. At the north-east end of the easterly chamber, investigators found a construction shaft that had been blocked with stones, most likely the original access point used when the souterrain was being built and then sealed once the work was complete. The site was investigated and recorded by Ryall in 2003.