Its full extent has never been determined. What it represents, however, is reasonably well understood: this is a fulacht fia, one of the most common and yet most quietly mysterious monument types in the Irish landscape. A fulacht fia is a prehistoric cooking site, typically identified by a mound of fire-cracked stone left behind after repeated heating. The usual method involved heating stones in a fire, then dropping them into a water-filled trough to bring it to boiling point, a process efficient enough to have been used for centuries during the Bronze Age.

The proximity to a spring is no accident. Fulachtaí fia, as they appear in their hundreds across Ireland, are almost always found close to a reliable water source, and the spring at Agharinagh fits the pattern precisely. The burnt and shattered stone that accumulates over time, discarded after each use when it becomes too fragile to reheat effectively, forms the characteristic horseshoe-shaped mound that survives in the ground long after everything else about the site has disappeared. Here, the spread of burnt material has been noted but not fully excavated or mapped, which means the site remains, in a practical sense, only partially read. Its boundaries, its age, and the precise character of its use are still open questions.