These low, horseshoe-shaped mounds of fire-cracked stone and dark, charred soil are the remains of ancient cooking sites, typically Bronze Age in origin, where water was heated by dropping stones that had been made red-hot in a nearby fire into a trough or pit. The one at Ranaleen, in County Kerry, is a quiet example of this widespread but still not fully understood tradition.

The fulacht fia as a monument type appears throughout Ireland, but Kerry has a particularly dense concentration of them, scattered across boggy ground and river margins where the necessary water supply was close at hand. The standard interpretation is that they served as outdoor cooking facilities, perhaps used seasonally by groups moving livestock across the landscape, though some researchers have proposed other uses including bathing, brewing, or textile processing. The mounds themselves are the accumulated debris of repeated use, stone after stone discarded once it had cracked beyond further service in the fire. Over centuries, these rejected fragments built up into the low crescents that survive today, often preserved beneath blankets of peat that formed long after the fires went cold.