The site is a caher, a type of stone ringfort built with dry-laid masonry walls rather than earthen banks, and it had presumably stood for the better part of a millennium before being pressed into this secondary use. The conversion left its mark. When the antiquarian John Windele visited in 1848, he recorded that the inner face of the enclosing wall had been substantially rebuilt in the modern period, and subsequent investigation has found it difficult to separate original stonework from later intervention at the eastern and southern stretches.

The structure itself, known in Irish as Cathair Dónall, sits on a rock outcrop that drops away sharply on its northern side and looks out towards Darrynane Bay to the south-west. Its enclosing wall is built around a rubble core, faced on both sides with well-laid drystone masonry, and averages 3.6 metres wide at the base. At the north, where collapse and later meddling have been least disruptive, the external face survives to a full five metres in height and retains a pronounced batter, meaning the wall leans slightly inward as it rises, a technique common to substantial cahers. The interior, roughly 25 metres across, is raised above the surrounding ground. A five-metre entrance passage at the south-west, about 2.5 metres wide, provided the original access point, and a large flat slab leaning against a later wall nearby may once have served as its lintel. Along the northern inner face, a shallow recess nearly five metres long appears to be an original feature rather than a later addition, and in the north-western quadrant, upright slabs and traces of drystone walling may mark the footprint of a former hut. T. J. Westropp, writing in 1912, mentioned a holed stone at the site, but it can no longer be identified among the remaining fabric.