The site only came to light in 1986 when the roof of one of its chambers collapsed, an abrupt and accidental disclosure of something that had been sealed beneath the soil for centuries.

A souterrain is an artificial underground structure, typically built during the early medieval period in Ireland, consisting of one or more chambers connected by low passages and lined or roofed with stone. They are generally understood to have served as places of refuge, cool storage, or concealment, and they appear across much of the Irish countryside, often associated with nearby settlement activity. The Ballynacorra example is modest in scale: the chamber runs approximately 4.7 metres in length and just 0.6 metres in width, roofed with capstones and by the time of its recording considerably filled in with sediment. At some point after its discovery, a narrow trench was cut across the chamber in a north-to-south direction, presumably to investigate the structure's extent or condition.