They typically appear as low, horseshoe-shaped mounds of fire-cracked stone, the accumulated debris of repeated cycles of heating rocks and plunging them into water-filled troughs. The one at Carrownaraha in County Mayo is one such site, quiet in a field and easy to overlook, though it connects the local ground to a pattern of activity stretching back to the Bronze Age.

The term fulacht fia translates loosely as "cooking place of the deer" or "cooking place of the wild," and for much of the twentieth century that culinary interpretation dominated, with archaeologists envisioning communal outdoor feasts. More recent thinking has widened the possibilities considerably, with brewing, textile processing, and bathing all proposed as alternative or additional functions. What remains consistent across these sites is the basic technology: stones heated in a nearby fire, then transferred to a water-filled trough until the water boiled, with the shattered, thermally shocked stones discarded to either side to form the characteristic mound. Dates recovered from excavated examples across Ireland cluster mainly in the Bronze Age, roughly 2000 to 500 BC, though some sites show use into the Iron Age.

Carrownaraha itself is a townland in Mayo, and the presence of a fulacht fia there places it within a broader concentration of prehistoric activity that the boggy, marginal landscapes of the west of Ireland have preserved unusually well. The waterlogged conditions that make such terrain difficult to farm are precisely what protect organic material and ancient earthworks from the plough.