A cashel is a stone-walled ringfort, the kind of early medieval enclosure built to protect a farmstead and its inhabitants, and this one is roughly circular with a diameter of around nineteen metres. But its fabric tells several different stories at once, with different phases of building visible in the same structure. Part of the perimeter is a double wall of large stones set upright on their ends, rising to between 0.7 and one metre on the outer face. Elsewhere the boundary becomes a bank of stone and earth, and elsewhere again it reduces to barely visible foundations only a few centimetres wide. A later wall was added to the outer face on the north-north-east to south-east arc, and a boundary wall cuts straight through the eastern half of the interior from north to south. Whatever the original enclosure was built for, later generations kept coming back and adding to it.

The site sits within a multiperiod field system, meaning the landscape around it preserves traces of agricultural organisation from several different eras, layered one over another. This broader pattern of use was already legible on the Ordnance Survey six-inch maps of 1842 and 1916, where the cashel was recorded under the deliberately cautious label of "Earthwork", the surveyors acknowledging something significant without committing to an interpretation. A second cashel lies approximately one hundred metres to the north-north-west, suggesting that whoever occupied this part of Clare was prosperous or numerous enough to sustain more than one such enclosure in close proximity. The structure at Cahermacun is described as moderately well to poorly preserved, which in archaeological terms means that a trained eye can still trace its logic even where the masonry has collapsed or been robbed for later use.