What makes Cahernasbunnog, sitting on a low limestone rise in Bushfield, County Mayo, quietly remarkable is less what it looks like now and more what it once was. A concrete farmyard, complete with silage pit and outbuildings, has consumed the entire south-eastern edge of the site. The eastern half of the enclosure has been stripped away entirely, truncated to a bare linear scarp. What remains on the western side is a series of low, sod-covered humps and ridges, nettle-choked and easy to walk past without a second glance, yet those hummocks preserve the ghost of something genuinely ambitious.

When the antiquary Knox recorded the site in 1911, it was already in serious decline, yet he was still able to describe what the previous generation had seen: walls standing as high as a man, a great inner ring wall some four metres thick and built in three distinct sections, with stone faces and rubble fill layered outward one against the other, and beyond that at least two further enclosing walls separated by narrow spaces. By the time of his visit, most of this had been robbed for building material. The cashel appears by name on the Ordnance Survey six-inch maps of 1838 and 1930, so the name Cahernasbunnog was well established long before the modern damage. Today, careful observation on the western arc of the site reveals the basal courses of massive horizontally-laid limestone slabs that once formed the outer face of the innermost wall, and beyond them a fosse, a second wall, a berm, and upright limestone slabs that likely represent the outermost ring Knox described. The interior, slightly raised above the surrounding pasture because the builders exploited a natural bedrock outcrop, also contains pits that appear to be the result of relatively recent stone quarrying rather than anything ancient.

The site sits in open pasture with broad views over the gently undulating limestone grassland of this part of Mayo. The perimeter is ringed with hawthorn bushes, nettles, and thistles, which mark the line of the vanished walls more reliably than the stonework itself in several places. The contrast between what Knox described in 1911 and what the ground actually shows today gives the place a particular quality: the archaeology is difficult to read, but the process of loss is legible at every turn.