A fulacht fia, the term for a type of prehistoric cooking or processing site found widely across Ireland, came to light in 2007 in circumstances that made its original function immediately legible. At the moment of excavation, water from two converging streams was seeping steadily into the stone-lined trough, keeping it perpetually full, just as it would have been when the site was in active use.

The excavation, carried out under licence numbers E3391 and E3645, revealed a mound of heat-shattered sandstone roughly eight metres east to west and ten metres north to south, with the characteristic mix of charcoal concentrated towards the centre and cleaner material towards the edges. This crescent or horseshoe-shaped spread of fractured stone is the diagnostic signature of a fulacht fia: rocks would have been heated in a nearby fire, then dropped into a water-filled trough to bring the water to boiling point. The trough itself was earth-cut and roughly rectangular in plan, measuring just under two metres by one and a half, with steep sides and a flat base, filled over time with a compact deposit of black sandy silt, charcoal, and the same shattered stone that surrounded it. Fragmentary remains of a hearth were found about one and a half metres to the north-east, presumably where the stones were heated before being transferred to the water. What is particularly striking about Ballylusky is that it was not an isolated installation. Three further fulachta fia were excavated approximately one hundred metres to the north, on the opposite bank of the stream, suggesting this stretch of watered, low-lying ground was returned to repeatedly, perhaps across generations, by people who knew exactly what the landscape offered them.