The mound is only about forty centimetres high, easy to miss underfoot, but its shape and contents tell a specific story about how people prepared food, or possibly heated water for other purposes, thousands of years ago.

A fulacht fia, sometimes called a burnt mound, is a type of archaeological site found in enormous numbers across Ireland and Britain, typically dating from the Bronze Age, though some examples are earlier or later. The name, from the Irish, is traditionally associated with the idea of a cooking place, and the standard interpretation is that stones were heated in a fire, then dropped into a water-filled trough to bring it to boiling point. The discarded stones, cracked and shattered by repeated heating and cooling, were piled to the side, gradually forming the characteristic horseshoe or crescent shape. At Foildarrig, that crescent measures roughly 7.2 metres from east to west and 3.8 metres north to south, with an opening 1.4 metres wide facing north towards the stream that would have supplied the water. The mound itself is composed of exactly what the type-site demands: heat-shattered stones mixed with charcoal-enriched, darkened soil. Where the stream has cut through its banks, burnt material is visible in section on both sides, suggesting the activity extended a little beyond the visible mound surface.