But these small humps of burnt stone and ash are the remains of a fulacht fia, a type of prehistoric cooking or processing site found in considerable numbers across Ireland. The principle was straightforward: stones were heated in a fire and then dropped into a water-filled trough, bringing the water to a boil. Over repeated use, the shattered and fire-cracked stones were raked out and piled beside the trough, forming the characteristic horseshoe-shaped mound that survives today.

The two examples at Donaguile are almost conjoined, sitting side by side in a flat, low-lying area between two sloping hillocks. Each mound measures roughly two metres by one and a half metres, and neither stands more than thirty centimetres high. Both have a central depression measuring about one and a half metres by seventy-five centimetres, the ghost of the original trough. A stream runs just two metres to the north, which would have made the location well suited to whatever activity the site supported. The mounds are composed of burnt stone and ash, the accumulated debris of that repeated heating and cracking. When the surrounding land was planted with forestry in 1988, a clearing with a buffer zone of approximately ten metres was maintained around the monuments, preserving them within what is now a pocket of open ground inside the plantation.