It measures roughly seven metres across at its narrowest and just over twelve metres at its widest, rising no more than about 0.7 metres above the surrounding wetland. That unassuming shape is what identifies it as a fulacht fia, a type of prehistoric cooking or processing site found widely across Ireland and Britain, typically consisting of a horseshoe-shaped or oval mound of fire-cracked stones discarded after repeated heating. The standard interpretation is that stones were heated in a fire and then dropped into a water-filled trough to bring it to the boil, though debate continues about whether these sites were used primarily for cooking, bathing, brewing, or some combination of activities.

What makes the Larkhill site particularly interesting is its setting within a cluster. Two further possible fulachtaí fia lie close by, one approximately ten metres to the north-east and another roughly forty metres to the east. The concentration of sites around a single marshy pool suggests repeated, possibly sustained use of this waterlogged landscape over time. Fulachtaí fia are generally dated to the Bronze Age, broadly between around 1500 and 500 BC, though some examples have produced earlier or later dates. The presence of standing water would have been essential to their function, and low-lying boggy ground like this, inconvenient for farming or settlement, was precisely the kind of terrain where such activity tended to cluster.