It is a fulacht fia, a type of prehistoric cooking site found in considerable numbers across Ireland, typically dated to the Bronze Age. The basic principle involved heating stones in a fire, dropping them into a water-filled trough until the water boiled, and using the resulting heat to cook meat. The broken, fire-cracked stones were then discarded, and over centuries these dumps accumulated into the distinctive horseshoe-shaped mounds that survive today. This one, roughly subcircular and about twelve metres across, rises only thirty centimetres above the surrounding ground, its modest profile suggesting long centuries of gradual compression into the soft earth.

What makes Rathcobane somewhat more interesting than a mound alone is what surrounds it. On its north-western side, close to the stream, there is a shallow indentation edged by three possible kerbing stones, likely the location of the original trough. Several stones of comparable size protrude from the western edge of the mound. More intriguingly, approximately eleven metres to the west, a line of stones runs for about fifty metres in a north-east to south-west direction through the boggy ground, most of them set parallel to one another. This alignment is cut short by a laneway to the south, and on the far side of that lane a separate arrangement of stones runs east to west for around twenty metres, these ones set side by side rather than parallel. Whether these stone lines are directly associated with the fulacht fia, or represent something earlier or later, is not recorded, but their relationship to the mound and the stream gives the site a slightly more layered quality than the mound itself might suggest.