They appear as low, horseshoe-shaped mounds, typically found near water, and are generally dated to the Bronze Age, roughly 1500 to 500 BC. The working theory for most of them is that they served as cooking sites: stones would be heated in a fire, then dropped into a water-filled trough until the water boiled, allowing meat to be cooked. Experiments have shown the method works surprisingly well. The one at Cloonnagleragh, in County Mayo, is one of countless such sites quietly occupying the margins of fields and bogland across the country, largely unnoticed by anyone not specifically looking for them.

The name fulacht fia translates roughly from Irish as "cooking pit of the deer" or "cooking place of the wild animal", though some scholars have argued the word fiadh here may refer to a landless or outlaw class rather than game animals, suggesting these sites may have served itinerant or marginal groups rather than settled communities. Others have proposed uses beyond cooking, including hide-tanning or even bathing. The debate has never been fully resolved, which gives every surviving example a certain openness as an object of curiosity. Mayo, with its extensive boglands, preserves a significant number of these monuments; the wet, acidic conditions that make the landscape agriculturally difficult have also protected what lies beneath the turf.