The best preserved of the group is a horseshoe-shaped mound, a form typical of fulachtaí fia, the prehistoric cooking sites found in great numbers across Ireland. The horseshoe shape is characteristic: animal hides or wooden troughs were filled with water, heated stones were dropped in to bring it to a boil, and the cracked, fire-shattered fragments of those stones were heaped to the sides over repeated use, gradually building up the distinctive curved mound. This one measures roughly 12.6 metres north to south and 6.2 metres east to west, rising to a maximum height of about 0.6 metres, which counts as well preserved for a monument type that has often been ploughed flat or simply overlooked.

What makes the Coolnatullagh site particularly interesting is not the mound alone but its setting and its company. The three fulachtaí fia here all fall within a multi-period field system, meaning the landscape around them carries traces of human organisation spanning more than one era. The stream that supplied water for the cooking process rises just to the north, making the location a logical and deliberate choice rather than an accident of survival. Low hazel-clad limestone bluffs close in from the west, north, and east, giving the shallow valley a sheltered character. Jones, Carey, and Hennigar noted the cluster in 2011, and the proximity of the three monuments to one another along a single watercourse suggests this was a place returned to repeatedly, possibly across generations.