The structure is a fulacht fia, a type of monument found widely across Ireland and typically associated with the Bronze Age. The form is distinctive: a mound of fire-cracked stones arranged in a horseshoe shape around a central trough. The basic method involved heating stones in a fire, then dropping them into a water-filled pit to bring it to boiling point, a surprisingly efficient technique that experimental archaeology has repeatedly shown to work. The example at Farranastack is described as substantial, which sets it apart from the many smaller or more fragmentary sites of the same type.

Fulachta fia are among the most common prehistoric monument types in Ireland, yet they remain quietly overlooked, partly because they tend to survive as low, unassuming mounds in wet or marshy ground. Their very ordinariness is part of what makes them interesting: these were not ceremonial constructions or burial monuments, but functional places where people gathered to prepare food, and possibly to engage in other communal activities. The horseshoe shape at Farranastack is the classic form, the open end typically facing a water source, whether a stream, spring, or boggy hollow. The site was recorded by Dunne in 2000.