It is, in fact, the remains of a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland, typically dating from the Bronze Age. The mound measures roughly 18.4 metres north to south and 14.9 metres east to west, rising just 0.6 metres above the surrounding ground, which gives some sense of how much fire-cracked stone can accumulate over repeated use of a single spot.

A fulacht fia functioned, in its simplest form, as an outdoor boiling pit. Water was collected in a trough, often timber-lined, and heated by dropping stones that had been fired in a nearby hearth directly into the water. The stones, subjected repeatedly to this thermal shock, crack and fracture, and it is the discarded accumulation of these broken fragments that builds up over time into the characteristic horseshoe-shaped mound seen at sites like this one. The three depressions visible in this particular mound are likely the result of more recent, informal digging into it rather than any ancient feature. What makes the Killabraher site especially notable is that a second fulacht fia lies approximately 100 metres to the southwest, suggesting this area saw sustained or repeated prehistoric activity rather than a single, isolated episode of use. The proximity of a drain on the northwest side is consistent with the general pattern of these sites appearing near water sources, which were essential to the whole process.