The promontory fort at Ceathrú Na Gcloch in County Mayo now sits effectively marooned, its interior visible from the land but entirely unreachable, which lends the whole place an oddly suspended quality. It occupies the highest point of a large north-facing headland, flanked by sheer cliffs, with a small inaccessible cove to the east and a neighbouring promontory that, for reasons unknown, was never fortified at all.

What the collapse of the isthmus has left behind is still remarkable in scale and complexity. The landward defences consist of five banks and four ditches, curving across the neck of the headland in a layered system that speaks to considerable effort and, presumably, a serious concern with keeping people out. The outermost ditch alone measures 14 metres wide at its base and drops 4.5 metres below the adjacent bank, with steep sides that still show traces of stone revetting. A souterrain, an underground passage cut into the rock with an entrance roughly 0.8 metres square, survives near the eastern end of the outermost bank, alongside a collapsed circular hut site. A souterrain of this kind typically served as a place of concealment or storage, and this one went unrecorded by the antiquarian Thomas Johnson Westropp when he visited in 1904, suggesting it was either hidden or simply easy to miss. Westropp did note a feature he called a "well-marked gangway"; a broad earthen and stone bank, now 10 metres wide and running 120 metres from the western cliff edge, may be what survives of it. A rock-cut trench running parallel to the western cliff, between 2 and 4 metres deep, has no confirmed purpose but may once have formed part of the original entrance.

The site lies in mountainous bog and is not easily reached, and with the isthmus gone the interior cannot be entered at all. The view from the headland, however, is unobstructed, and Westropp's brief account from 1904 suggests the defences have changed little in the intervening century.