It measures roughly ten metres north to south and eight and a half metres east to west, rising to about one and a half metres at its highest point. Its opening faces east, towards a marshy patch of ground, and a sheep track has worn away part of its north-western edge over the years. Forty metres to the west-north-west, a second, near-identical structure occupies the same hillside.

What looks like an unremarkable grassy mound is in fact a fulacht fia, the remains of a Bronze Age cooking site. The term refers to a particular type of outdoor hearth arrangement, typically consisting of a trough dug near a water source, a fire used to heat stones, and those stones dropped into the water to bring it to boiling point. The discarded, heat-shattered stones gradually accumulated into the characteristic horseshoe shape seen here, with the open end facing the water source or marshy ground that supplied the trough. These sites are remarkably common across Ireland, with thousands recorded, yet their very ordinariness is part of what makes them interesting. They are the archaeological residue of repeated, practical activity, cooking or possibly bathing or industrial processes, carried out over generations somewhere between roughly 1500 and 500 BC. The two examples on Mangerton sitting so close together suggest this part of the mountain slope was used regularly, perhaps seasonally, by people moving livestock through the uplands.