It measures roughly fourteen metres long, eight metres wide, and half a metre high, and it is made almost entirely of burnt stone and charred material, the accumulated debris of prehistoric cooking carried out across many generations.

This is a fulacht fia, a type of monument found in extraordinary numbers across Ireland, particularly in low-lying or marshy ground near water sources. The basic principle is ancient and practical: stones were heated in a fire, then dropped into a water-filled trough, bringing the water rapidly to a boil. Meat could be wrapped and cooked this way, and experiments have shown the method to be surprisingly efficient. Over time, the cracked and spent stones were raked out and piled to the side, building up the characteristic horseshoe-shaped or oval mound that survives long after the trough itself has silted over or decayed. Ireland has thousands of these sites, most dating to the Bronze Age, roughly 2000 to 500 BC, making them one of the most common prehistoric monument types on the island. The one at Beennamweel follows the familiar form, its mound of fire-shattered material now softened by turf and vegetation into something that looks almost geological rather than human in origin.