It measures roughly eleven and a half metres along its longer axis and rises less than a metre from the surrounding ground. That modest profile is the whole point. This is a fulacht fia, a type of prehistoric cooking site found in their thousands across Ireland, and the mound itself is essentially the accumulated debris of countless fires and broken stones.

The mechanics of a fulacht fia are straightforward but quietly ingenious. A trough, usually timber-lined or stone-lined, was filled with water. Stones were heated in a nearby fire, then dropped into the trough to bring the water to a boil. The repeated heating and rapid cooling caused the stones to crack and shatter, and the discarded fragments built up around the site over time into exactly the kind of low, scorched mound visible here at Coolies. The horseshoe shape is typical of the form; the open end of the curve generally faced the water source, allowing easy access to the stream. At this site, a narrow grass path, roughly seventy centimetres wide, cuts across the south-eastern portion of the main mound, and this has effectively separated off a smaller secondary mound to the south-east. That smaller rise includes a roughly circular raised area about two and a half metres in diameter, edged along its southern arc by two small rocks. Whether the path is ancient or a more recent intrusion across the site is not recorded, but its effect on the mound's shape is clearly visible in the dimensions.