A cashel is a type of ringfort defined by a drystone enclosing wall rather than an earthen bank, and this one at Castlebarnagh still holds enough of its original fabric to reward a careful look. The site is oval, roughly 30 metres north to south and just under 25 metres east to west, and the wall that defines it, around 1.4 metres thick, has survived in varying states of completeness depending on which arc you examine.

The most telling section is on the western side, where five courses of stonework survive to a height of 1.6 metres and appear to rest on a low earthen scarp. Here, at least, the original scale of the structure is still legible, the basal courses incorporating large limestone blocks and boulders that speak to the effort originally invested in its construction. The northern arc tells a different story: the external face drops to a maximum height of 0.6 metres and is capped with small loose stones, most likely the accumulated debris of generations of field clearance. The inner face on the southern arc survives to between one and 1.5 metres, but the rough, small-stone construction visible there suggests significant rebuilding at some point in the modern era. There is no clearly defined entrance gap anywhere in the circuit, and several areas of slumping at the southeast, west-southwest, and north-northwest have left the wall ambiguous in places. A loose heap of stones, roughly 2.8 metres by 2 metres, sits piled against the inner face on the south side, its origin unclear. The ridge position is worth noting: the site commands a good view out over the undulating landscape, particularly to the northwest and northeast along the course of a broad, flat stream valley, a sightline that would have mattered to whoever chose this spot.