It measures roughly fifteen metres north to south and thirteen metres east to west, rising no more than about half a metre at its highest point on the western side. Beneath the grass, however, the mound is composed of angular sandstone fragments packed into dark, charcoal-rich soil, the characteristic signature of a burnt mound, a type of prehistoric site found widely across Ireland and Britain.

Burnt mounds are among the more enigmatic features of the Irish landscape. They consist of heat-shattered stone and charred material, accumulated through repeated cycles of heating stones in fire and plunging them into water, most likely to boil it. Whether this was for cooking, bathing, textile processing, or some combination of uses is still debated, but the practice was widespread during the Bronze Age. The Dooncastle example sits on slightly elevated ground at the margins of low-lying wet and boggy land, a setting that is entirely typical of the type, as access to water was presumably central to whatever activity the mound served. The western edge slopes noticeably down towards an area of wet ground, reinforcing this connection to the surrounding wet landscape. The eastern side of the mound is less distinct, apparently cut through by a north to south field wall that now runs along the border of a modern road, meaning part of the original extent has likely been lost.