That low, discoloured patch in the soil is what remains of a fulacht fia, one of the most common yet persistently mysterious monument types in the Irish archaeological record.

Fulachtaí fia (the plural form) are prehistoric cooking sites, found in their thousands across Ireland, typically dating to the Bronze Age, from around 1500 BC onwards. The standard interpretation is that they functioned as outdoor boiling hearths: a trough, often timber-lined, was filled with water, then stones were heated in a nearby fire and dropped into the trough to bring the water to a rapid boil. The shattered, heat-fractured stones were discarded to the side, building up over time into the characteristic horseshoe-shaped mound of blackened rubble that archaeologists recognise today. At Coolvallanane Beg, ploughing has disturbed whatever mound once stood here, spreading the burnt material across the ground surface and making the site most legible as a broad, scorched stain rather than a standing earthwork.