A fulacht fia is a prehistoric cooking site, typically consisting of a mound of fire-cracked stone accumulated beside a trough, usually timber-lined, into which water was poured and heated by dropping in stones from a fire. Thousands of them survive across Ireland, most dating to the Bronze Age, and yet the Killavallig example is so thoroughly overgrown that even its characteristic burnt and shattered stone, the material signature that usually confirms such sites, cannot be identified on the ground.

What is known comes largely from local knowledge rather than excavation or survey. The site lies approximately forty metres to the northwest of a nearby stream, a detail that fits neatly with what is understood about fulachtaí fia in general: they are almost invariably found close to a water source, since the whole process depended on a reliable supply. The boggy, low-lying ground around Killavallig is precisely the kind of terrain where these monuments tend to cluster, waterlogged conditions having helped preserve the mounds across several millennia even as the same conditions make them difficult to investigate. Without clearance of the overgrowth, the extent and condition of the site remain uncertain.