The sudden collapse exposed a souterrain, an underground passage or chamber cut from the earth, of the kind constructed throughout early medieval Ireland, typically associated with ringforts and used for storage, refuge, or both. The opening left behind is roughly square, about a metre across in each direction, dropping into an earth-cut chamber that has remained inaccessible since its accidental discovery.

Souterrains were built without mortar or formal engineering, relying instead on carefully placed stone lintels or, in earth-cut examples like this one, the stability of the surrounding subsoil. They survive in considerable numbers across Munster, though most are known only because the land above them gave way in similar circumstances, to livestock, machinery, or simply the slow settling of centuries. The Teereeven example sits in pasture on a north-facing slope, which is consistent with the agricultural landscape that has preserved, and occasionally swallowed, countless such features across Cork. Its precise age is unknown, but souterrains of this type are generally associated with the early medieval period, roughly the sixth to twelfth centuries.