The depression is stone-filled, its shape tracing the ghost of a souterrain, an underground stone-built passage or chamber constructed during the early medieval period, typically associated with ringforts and used for storage, refuge, or both.

The souterrain sits within a ringfort, a type of enclosed farmstead that was the dominant settlement form in early medieval Ireland, generally dated to between roughly the sixth and twelfth centuries. The form of the collapsed passage can still be read in two arms: the longer running north to south at around eleven and a half metres, and a shorter arm of just over nine metres branching off at the north-east end and running roughly west-south-west to east-north-east. That L-shaped plan is fairly characteristic of souterrain construction, where a secondary passage or chamber was added off the main run, sometimes to serve as a separate storage space or to complicate access for anyone attempting to enter uninvited. The fact that it is now visible only as a depression filled with stone suggests the roof structure, likely large capstones laid across the passage walls, has long since given way.