Roughly thirteen metres from north to south and eleven metres across, rising only half a metre from the surrounding ground, it is composed almost entirely of burnt and fire-cracked stone, the accumulated debris of repeated ancient cooking. This is a fulacht fia, one of the most common prehistoric monument types found across Ireland, and one of the least understood in terms of the social life it once served.

Fulachtaí fia, as a class of monument, are generally associated with the Bronze Age, roughly 2000 to 500 BC, though some examples are older or more recent. The typical arrangement involved a trough dug into the ground, often timber-lined, which was filled with water and heated by dropping fire-cracked stones into it. Once the stones fractured and cooled they were useless for further heating, and were discarded in a heap nearby. Over generations of use, those heaps became the horseshoe-shaped or oval mounds archaeologists now find dotted across the Irish landscape, often close to streams or marshy ground where water was readily available. What the troughs were actually used for remains debated: cooking is the most widely accepted explanation, though brewing, bathing, and textile processing have all been proposed with varying degrees of supporting evidence. The example at Knockcloona fits the general pattern, a modest but legible accumulation of scorched material in agricultural land, the kind of site that survives precisely because it is low-lying and not obviously worth disturbing.