It measures ten metres long, seven metres wide, and stands about eighty centimetres high. It is, in all likelihood, several thousand years old, and it was built for the entirely practical purpose of cooking.

A fulacht fia is a type of prehistoric cooking site found in enormous numbers across Ireland, particularly in low-lying, wet ground near water sources. The basic method involved heating stones in a fire until they were intensely hot, then dropping them into a water-filled trough to bring the water to a boil. Meat, wrapped in straw or placed directly in the water, could then be cooked. The stones, fractured and spent from repeated heating and rapid cooling, were discarded to the side of the trough over time, building up the characteristic horseshoe or crescent-shaped mound that survives today. The hollow of the horseshoe typically marks where the trough once sat. These sites are most commonly dated to the Bronze Age, roughly 1500 to 500 BC, though some examples fall outside that range. The Rylane example fits the classic profile almost precisely: the wet, marshy setting beside a river, the curved mound of burnt and broken stone, the modest but unmistakable profile rising from the ground.