A souterrain, the term for the kind of man-made underground structure commonly associated with Early Medieval ringforts in Ireland, it was uncovered entirely by accident in 1980 during land reclamation works, when the displacement of a roofing lintel broke the surface and opened a gap into the darkness below.

What the subsequent inspection revealed was a narrow passage running roughly northeast to southwest, measuring 4.6 metres in length, around 0.75 metres wide, and between one and 1.2 metres high. The walls were of drystone construction, meaning stones laid without mortar, and the ceiling was formed from flat lintel slabs laid across the top. The northeast end had been blocked by collapsed soil. More intriguing was what lay at the other end: a small opening known as a creep, a deliberately low and narrow gap between sections of a souterrain, which would have required anyone passing through it to crouch or crawl, presumably as a defensive measure. This creep led into a rectangular chamber beyond, though a blockage prevented anyone from actually entering it. The passage was recorded, and the access hole was then covered over again. Today, nothing at ground level betrays that any of this exists.

The souterrain sits within a ringfort, a type of enclosed farmstead dating broadly to the Early Medieval period, roughly the fifth to twelfth centuries, which were often furnished with souterrains for storage, refuge, or both. Because the access point was sealed after the 1980 inspection and no surface trace remains, there is nothing for a visitor to observe directly.