It is not a burial, not a fort, and not the ruin of any building. It is a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland, and this one at Tooreennagrena preserves its shape with quiet clarity.

A fulacht fia typically consists of a mound of fire-cracked and heat-shattered stone built up over many centuries of use beside a water source. The process involved heating stones in a fire, then dropping them into a water-filled trough to bring it rapidly to a boil, the shattered and spent stones gradually accumulating into the characteristic horseshoe shape that frames the trough. The Tooreennagrena example measures roughly twelve metres east-northeast to west-southwest and eleven metres north-northwest to south-southeast, rising to about 1.1 metres at its highest point. Its opening, about 1.8 metres wide, faces northwest. What makes this particular site a little more legible than many is the additional trail of burnt material that extends westwards from the western arm of the mound for approximately 6.7 metres, reaching a maximum height of 0.4 metres. This kind of spread suggests sustained activity and perhaps repeated clearance or accumulation beyond the main mound. The location in marshy ground close to a watercourse is entirely typical; access to a reliable water supply was essential to how these sites functioned.