A fulacht fia is, at its most basic, an ancient outdoor cooking site, typically consisting of a horseshoe-shaped mound of fire-cracked stone built up beside a trough or pit. Water would have been heated by dropping stones into the trough, the stones fracturing over time from repeated thermal shock and accumulating into the characteristic mound. Thousands of these sites have been identified across Ireland, yet Cloonsillagh's example survives now only as a grass-covered spread of burnt material, the residue of what was once a more substantial feature.

The mound itself was levelled before 1973, according to local knowledge, which places its destruction sometime in the mid-twentieth century, most likely as a consequence of agricultural improvement. This was not unusual. Across Ireland, the postwar decades saw significant land clearance and drainage work that removed or damaged countless monuments of this kind. What remains at Cloonsillagh is effectively a scatter, the dark spread of heat-shattered stone and charcoal still faintly legible in the pasture where the mound once stood. Fulachtaí fia are generally associated with the Bronze Age, roughly 2000 to 500 BC, though some have produced dates stretching into the Iron Age. Their exact social function, whether communal cooking, the processing of hides, or something else entirely, continues to be debated among archaeologists.