It is easily missed, heavily overgrown, and measures roughly eleven metres long by four metres wide. Yet its kidney shape, the characteristic curve of its opening facing south, marks it out as a fulacht fia, one of the most widespread and enigmatic monument types in the Irish landscape.

Fulachtaí fia are the remains of ancient cooking sites, found in their thousands across Ireland and dating primarily to the Bronze Age, though some continued in use into later periods. The typical arrangement involved a trough dug into the ground, often timber-lined, which was filled with water. Stones were heated in a nearby fire, then dropped into the trough to bring the water to a boil; meat could then be cooked by immersion. The spent, shattered stones were discarded to the side, building up over generations into the characteristic horseshoe or kidney-shaped mound that survives today. The preference for marshy, waterlogged ground was practical rather than accidental; a high water table meant the trough refilled naturally, making these wet, unpromising spots the ideal location for what was essentially an outdoor kitchen. The example at Carrignamaddry fits this pattern closely, sitting in marshy ground with its modest but legible mound still holding its shape after what may be thousands of years of slow submersion and overgrowth.