This is a fulacht fia, a type of ancient outdoor cooking place found widely across Ireland, typically identified by a mound of heat-shattered stone and a water-filled trough into which those stones were dropped to bring the water to a boil. What makes Coolroe quietly notable is not the site in isolation but what surrounds it: two further fulachtai fia stood just a few metres to the east, and a broader area of prehistoric activity lay roughly eighty metres to the west, suggesting that this stretch of boggy ground beside the river was not an incidental stopping point but something more purposeful and repeatedly used.

The Coolroe fulacht fia was fully excavated in 1998 by archaeologist R. Gillespie, ahead of construction work by Mayo County Council on a sewage treatment plant, the kind of unglamorous infrastructure project that has, over the decades, revealed an enormous amount about prehistoric Ireland. The mound itself measured 11.2 metres east to west and 7 metres north to south, rising to just 0.3 metres in height, with a small trough, roughly 1.6 metres by 0.95 metres and 0.2 metres deep, set at its southern end. Among the finds recovered were a struck chert waste flake, fragments of bone, and a single piece of worked wood. These are modest objects individually, but together they hint at the full range of activities that may have taken place here: stone tool work, animal processing, and the shaping of wood, all within reach of a reliable water source.