It measures roughly fourteen and a half metres long, just over ten metres wide, and rises less than a metre from the surrounding ground. Unassuming to any passing eye, it is the remains of a fulacht fia, one of the most common yet persistently mysterious monument types in the Irish archaeological landscape.

Fulachtaí fia, found in their thousands across Ireland, are generally dated to the Bronze Age, though some remained in use into the early medieval period. The typical interpretation is that they functioned as cooking sites. The method involved heating stones in a fire and dropping them into a water-filled trough, bringing the water rapidly to a boil. The stones, cracked and spent after repeated heating and quenching, were discarded into a crescentic or oval mound around the trough, which is precisely the kind of feature visible at Killeen. The proximity to a natural water source, in this case a well set in marshy ground, fits the pattern almost exactly. Water was not incidental to these sites; it was the whole point. Some researchers have proposed alternative uses, from textile processing to bathing, and the debate has not fully settled, but the association with water and heat is consistent across the type. The burnt mound at Killeen, modest in height but substantial in footprint, represents the accumulated debris of what may have been generations of repeated use.