A souterrain is an underground stone-lined passage or chamber, typically associated with ringforts and built during the early medieval period, probably serving as a place of refuge, cool storage, or both. They were constructed by hand, roofed with large capstones, and then buried, leaving little trace at the surface.

The ringfort at Ballymackean, recorded in the archaeological inventory, is the broader context for this underground feature. Ringforts, which were enclosed farmsteads typically dating from roughly the fifth to the twelfth centuries, are among the most common archaeological monuments in Ireland, with tens of thousands surviving in varying states of preservation. Many contain souterrains, though their presence is not always easily confirmed without excavation or close local knowledge. In this case, awareness of the souterrain comes from local tradition rather than formal investigation, passed on through the kind of community memory that occasionally preserves details no official record would otherwise capture.