They appear as low, horseshoe-shaped mounds, typically found near water, and represent the scorched debris of a cooking method that dates back to the Bronze Age. The technique involved heating stones in a fire, then dropping them into a water-filled trough until the water boiled, a process that left behind great quantities of cracked and fire-shattered rock. The mound at Ballinrea, in County Cork, is one such site, sitting quietly in a county that contains more of these monuments than almost anywhere else in Ireland.

The precise function of fulachtaí fia has been debated for decades. Cooking is the most widely accepted explanation, and experiments have shown the method works efficiently for boiling large joints of meat. Some researchers have proposed additional uses including textile dyeing, hide preparation, or even bathing. Whatever their purpose, the sites cluster around the middle Bronze Age, roughly 1500 to 500 BC, and their sheer density across Munster suggests they were a routine feature of prehistoric life rather than anything ceremonial or exceptional. Cork alone holds hundreds of recorded examples, making each individual site part of an extraordinarily widespread pattern of human activity that is easy to overlook precisely because it is so commonplace.