It is a fulacht fia, a type of prehistoric cooking site found in considerable numbers across Ireland, and one of the more enduring puzzles in Irish archaeology. The basic principle is understood well enough: a trough, usually dug into the ground near a water source, was filled with water, and stones heated in a nearby fire were dropped in to bring it to the boil. The shattered, burnt stones were then discarded in a crescent-shaped heap around the trough. That heap is what survives at Cloghvoula, and across hundreds of similar sites throughout the country.

The mound here measures roughly 19 metres along its longer axis and just over 9 metres across, rising to a height of about a metre. Its opening, around 4 metres wide, faces to the northwest, and the whole structure sits precisely where you would expect it, immediately adjacent to a spring that would have supplied the water. A drain has cut into the northwestern side of the mound at some point, interrupting the otherwise intact profile. The abundance of burnt and shattered stone within these mounds is what makes them so recognisable in the landscape; the repeated heating and rapid cooling of the rock causes it to fragment, and over generations of use the discarded material accumulates into the characteristic horseshoe shape. What exactly fulachtaí fia were used for beyond boiling water remains a matter of debate, with cooking, textile processing, bathing, and brewing all proposed at various points.