It is, in fact, the remains of a fulacht fia, one of the most common yet persistently mysterious monument types in the Irish landscape. These horseshoe-shaped mounds, built up over centuries of repeated use, are the byproduct of an ancient cooking or industrial process in which water was heated by dropping fire-heated stones into a trough. The stones shatter with the thermal shock, and the discarded fragments accumulate into the characteristic crescent shape.

The Knockananig example measures eight metres in length and eight metres in width, rising to about 1.2 metres at its highest point, with the open end of the horseshoe, roughly 3.4 metres wide, facing south-east. It is heavily overgrown now, which is typical of fulachta fiadh that have survived inside forestry plantations, where bracken, moss, and the general density of undergrowth can make even a substantial mound easy to walk past without registering it. The proximity to a stream is entirely characteristic. Water was essential to the process, and the majority of these sites are found close to a reliable source. Fulachta fiadh are generally dated to the Bronze Age, though some continued in use or were reused much later, and their precise function, whether for cooking meat, brewing, bathing, or some combination of purposes, remains a matter of archaeological debate.