These are among the most common prehistoric monuments in Ireland, yet most people walk past them without a second glance. A fulacht fia typically appears as a low, horseshoe-shaped mound of burnt and shattered stone, often found close to a water source. The mound is the accumulated debris of repeated cooking, or possibly bathing or industrial activity, carried out over long periods during the Bronze Age. The method involved heating stones in a fire and dropping them into a water-filled trough until the water boiled, a process that eventually cracked and blackened the stones beyond reuse, leaving them to be discarded at the edges of the pit.

Thousands of these sites are recorded across Ireland, with particularly dense concentrations in Munster. Clare itself has a considerable number, scattered across bogland, field margins, and river valleys. The burnt mound at Derry is one such example, its precise dimensions and condition unrecorded in publicly available detail at present. What is known is the general character of such monuments: they are almost always Bronze Age in date, broadly spanning the period from around 1500 to 500 BC, and their proximity to wetland or running water is so consistent that modern archaeologists have used it as a rough locating principle. The sheer repetition of the fulacht fia across the Irish countryside suggests a practice that was entirely ordinary to the people who carried it out, which makes its strangeness to modern eyes all the more interesting.