It is, in fact, a fulacht fia, one of the most common yet least-understood monument types in the Irish archaeological record. These horseshoe-shaped mounds, built up over centuries of repeated use, are the debris of a cooking method that involved heating stones in a fire and dropping them into a water-filled trough until the contents boiled. The shattered, heat-fractured stone accumulates into a mound over time, and it is that mound, rather than any structure above ground, that survives.

Fulachtaí fia are found in their thousands across Ireland, concentrated particularly in low-lying, waterlogged ground, and most date to the Bronze Age, roughly between 1500 and 500 BC, though some examples span a wider range. The standard interpretation, associated largely with the experimental archaeology of M. J. O'Kelly in the mid-twentieth century, holds that they were cooking sites, capable of boiling a substantial joint of meat in a surprisingly short time using this stone-and-trough method. Other theories have proposed uses ranging from textile processing to bathing, and the debate has not been fully settled. What is consistent across sites is the combination of a burnt mound, a hearth, and proximity to a water source, a pattern that Culleen, set within the Clare landscape, would be expected to follow.