The original is a sub-circular mound, roughly fifteen metres north to south and just under fourteen metres east to west, but only about seventy centimetres high, worn low by centuries of exposure. Someone, at some point more recently, decided the summit needed marking more boldly, and built a new cairn directly in the centre of the old one. At nearly three metres tall with a circumference of almost eleven metres, the modern structure now dominates what the ancient one once defined.

Cairns of this kind, essentially mounds of piled stone raised over burials or as territorial markers, are among the oldest man-made features in the Irish landscape, typically associated with the Bronze Age or earlier. The fact that this one sits on a hilltop with a commanding view follows a pattern seen across Ireland, where elevated positions were chosen not just for visibility outward but for visibility inward, so the monument could be seen from the land below. What makes Coolcoulaghta quietly interesting is the layering: the modern cairn, presumably built by walkers or locals continuing an old tradition of marking high ground, has effectively buried part of the archaeological record it was placed upon, creating a small puzzle about where one period ends and another begins.