The example at Derrinlevaun, Co. Mayo sits quietly in flat, rush-grown pasture, presenting itself as a low kidney-shaped mound roughly sixteen metres from north to south and thirteen and a half metres from east to west, rising only about forty centimetres above the surrounding ground. At its centre is an elongated depression that opens to the west, and the southern lobe of the mound sits noticeably higher than the northern, giving the whole structure a lopsided, organic quality that distinguishes it from any accidental accumulation of soil.

A fulacht fia, in its simplest description, is the debris mound left behind by a prehistoric cooking or heating site. The process typically involved heating stones in a fire and then dropping them into a water-filled trough to bring the water to boiling point; the cracked, fire-shattered stones were then discarded to the side, building up over repeated use into exactly the kind of charcoal-dark, stone-dense mound visible here. The mound at Derrinlevaun is composed of a dense concentration of angular stone fragments packed into a matrix of black, charcoal-rich soil, which is the classic signature of this type of site. Most fulachtaí fia date to the Bronze Age, roughly 1500 to 500 BC, though the tradition may extend earlier or later in places. Their consistent association with wet, low-lying ground, as at Derrinlevaun, reflects the practical requirement for a reliable water supply close at hand. The site was brought to notice by Dwayne Jordan.