They appear as low, horseshoe-shaped mounds, typically found near water, and are generally dated to the Bronze Age, roughly 1500 to 500 BC. One such monument sits at Levallinree in County Mayo, a quiet mark on the land that most people would walk past without a second glance.

The prevailing interpretation of fulachtaí fia is that they served as outdoor cooking sites. The method involved heating stones in a fire, then dropping them into a trough of water to bring it rapidly to the boil. The burnt and shattered stones were discarded to the sides, and over time these accumulated into the distinctive mound that survives today. Some researchers have proposed alternative uses, including bathing, textile processing, or even brewing, and the debate has never been fully settled. The name itself, sometimes translated loosely as "cooking place of the deer" or associated with roving bands of hunters in early Irish literature, adds a layer of folklore to what is essentially a practical, workaday technology repeated at sites all across Ireland and Britain.