It measures sixteen metres long, eleven metres wide, and stands just under a metre high, its opening facing north. To a passing eye it might read as a natural rise in the ground, a hump of no particular consequence. It is, in fact, the remains of a fulacht fia, one of the most common prehistoric monument types in Ireland, and one of the least understood.

A fulacht fia is essentially a burnt mound, the accumulated debris of repeated episodes of heating stone in fire and plunging it into a water-filled trough to bring the water to a boil. The shattered, heat-spent stone was raked out and piled to the side, and over time those discards built up into the horseshoe or kidney-shaped mounds that survive today. They are typically found near water, which is precisely the case here at Flemingstown, where the mound sits on the west side of a stream. What they were actually used for remains a matter of debate among archaeologists: cooking is the most straightforward explanation, but brewing, textile processing, and bathing have all been proposed. The monuments date broadly to the Bronze Age, though some may be earlier or later, and Ireland has more of them than almost anywhere else in Europe.