What they had actually found was the remnant of a fulacht fia, a type of prehistoric cooking or processing site found widely across Ireland, typically consisting of a water-filled trough and a mound of fire-cracked stones built up over repeated use. The site at Lisnamuck is modest in scale, but its details are quietly telling.

The excavation, carried out ahead of a large-scale commercial development and recorded by Ó Maoldúin and Keeley, classified the site as Site 3. Beneath a charcoal-flecked layer of burnt stones, archaeologists uncovered two features: a subrectangular trough whose corners had been reinforced with five wooden stakes, and a small oval pit measuring 0.7 metres long, 0.6 metres wide, and 0.42 metres deep, with steep sides and a concave base. The trough would originally have held water, which was heated by dropping stones that had been fired in a nearby hearth directly into the liquid. The accumulation of those split and shattered stones, discarded after each use, is what produces the characteristic mound associated with these sites. What makes the Lisnamuck find particularly interesting is its context: two related sites lie nearby, a second fulacht fia roughly 77 metres to the northwest, and a burnt mound approximately 47 metres in the same direction. The clustering of these features suggests the area saw sustained prehistoric activity rather than a single isolated episode of use.