It is modest enough to walk past without a second glance, yet local tradition holds that this slight depression, roughly four metres east to west and three metres north to south, marks the entrance to a souterrain, an underground passage or chamber of the kind built throughout early medieval Ireland, typically for storage, refuge, or both.

The mound sits slightly north of centre within a rath, the Irish term for a ringfort, a class of enclosed settlement that was the dominant form of rural habitation in Ireland between roughly the fifth and twelfth centuries. Raths varied considerably in scale and complexity, and many were equipped with souterrains, stone-lined underground structures that made use of the constant cool temperature of the earth. At Lackancahill, no excavation appears to have confirmed what lies beneath, and the identification rests on the physical evidence of the hollow and its surrounding scatter of stones, combined with what people in the area have long said about the place. That combination, a suggestive surface feature and a persistent local memory, is itself a common way in which unexcavated souterrains are recognised across the Irish landscape.