But the dark, fire-scorched material visible where a stream has cut through it tells a different story. This is a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland, particularly in low-lying, water-adjacent ground. The basic principle involved heating stones in a fire, dropping them into a water-filled trough until the water boiled, and using that heat to cook meat. Over time, the cracked and spent stones were discarded into a heap, forming the characteristic horseshoe-shaped mound that survives today.

The mound at Derreenataggart measures fourteen metres in length and stands roughly 0.7 metres high, modest dimensions but enough to preserve a legible record of sustained, repeated activity. The stream that now bisects it has done inadvertent archaeological work, slicing through the accumulated debris and exposing the burnt material in cross-section on both sides of the bank. Most fulachtaí fia date to the Bronze Age, roughly 1500 to 500 BC, though some are earlier or later, and their precise social function has prompted considerable debate. Cooking is the leading interpretation, but uses ranging from textile processing to bathing have also been proposed by researchers over the decades.