It measures roughly 11.4 metres long, 11 metres wide, and rises just a metre above the surrounding pasture. To a passing eye it might read as an unremarkable rise in the ground, but the material beneath the grass is burnt stone and ash, the accumulated debris of repeated high-temperature activity carried out here perhaps three and a half thousand years ago.

The mound is a fulacht fia, a type of prehistoric cooking or processing site found in enormous numbers across Ireland, with several thousand recorded examples. The term, loosely translated from Old Irish, is sometimes rendered as "cooking place of the deer", though its precise original meaning is debated. The standard interpretation holds that a fulacht fia functioned as an outdoor boiling site: a trough, usually timber-lined, was dug nearby and filled with water, then heated stones were transferred from a fire into the trough until the water reached boiling point. The broken, fire-cracked stones were discarded into a mound beside the trough, which is exactly what survives today. This one at Clontead Beg fits the classic pattern closely, positioned beside running water on low-lying ground, the stream providing the ready supply that the whole process depended upon. Some researchers have proposed alternative uses for these sites, including hide-working, textile processing, or bathing, and the question has not been entirely settled.