It measures roughly ten and a half metres north to south and six metres east to west, and to the untrained eye it looks like nothing at all. To an archaeologist, it is a fulacht fia, one of the most common prehistoric monument types in Ireland, and one of the least understood.

A fulacht fia, sometimes called a burnt mound, is the debris left behind by an ancient cooking method. The broad idea, supported by experiment, is that stones were heated in a fire and then dropped into a water-filled trough, bringing the water rapidly to the boil. The cracked and spent stones were then raked aside, building up over time into the characteristic horseshoe-shaped or oval mounds that survive in their thousands across Ireland. The Glenalougha example follows the classic pattern, positioned beside a natural spring, which would have provided a reliable water source. Most fulachtaí fia date to the Bronze Age, roughly 2000 to 500 BC, though some appear earlier or later. The proximity to water is so consistent across these sites that it is considered almost a diagnostic feature. Why so many were built, and whether they served purely culinary purposes or had other functions, bathing or textile processing among them, remains a matter of ongoing debate among archaeologists.