A fulacht fia is typically a horseshoe-shaped mound of fire-cracked stone and dark, charcoal-rich soil, found near a water source and thought to date from the Bronze Age. The leading theory holds that they were cooking sites: stones were heated in a fire and dropped into a water-filled trough, bringing it rapidly to a boil. One such site sits at Inchincummer in County Kerry, an area whose placename hints at older, layered histories beneath the present landscape.

The mechanics of fulacht fia cooking, if that is indeed their primary function, have been tested by experimental archaeologists who found the method surprisingly efficient, capable of boiling a substantial volume of water within half an hour. Some researchers have proposed alternative uses, including textile dyeing, hide preparation, or even bathing, and the debate has not fully settled. What the mounds consistently record is repeated, deliberate activity over time, a place returned to again and again until the discarded heated stones accumulated into the low, distinctive humps that survive today. Kerry has a notable concentration of these sites, lying as it does in a landscape that has supported human settlement since deep prehistory.