This is a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland, typically dated to the Bronze Age. The standard interpretation is that stones were heated in a fire, then dropped into a water-filled trough to bring it to the boil, allowing meat to be cooked. The burnt and shattered stones, discarded after repeated heating and cooling, are what built up over time into the characteristic mound.

What makes the Capnagower site worth pausing over is its setting and its condition. It occupies the easternmost position among three fulachtaí fia arranged along the northern edge of an oblong peat basin, a shallow natural hollow running roughly east-northeast to west-southwest, enclosed on all sides by low hillocks and between fifteen and twenty-five metres wide. The basin itself would have held water readily, a practical necessity for this kind of site, and a small hillock at its eastern end has since been cut through by a drainage channel. At least four fulachtaí fia are known in the immediate area, another lying about thirty-one metres to the southwest. The one at Capnagower is considered the best defined and best preserved of those on Clare Island, its horseshoe plan still clear, the open end facing southeast toward the bog basin, and a slight saddle visible between the arms at the northwest. A turf-drying stack stands ten metres to the northeast, a reminder that this landscape has continued to be worked long after whoever built the fulacht fia was forgotten.

The site sits on a stony but flat terrace just above the limit of the cutaway peat, which is partly why it has survived so well. The surrounding bog, having been cut for fuel over generations, now forms a flat and somewhat featureless floor to the basin, making the mound itself stand out with unusual clarity against the open ground.