In the undulating pasture at Carns in County Sligo, the north-eastern quadrant of an early medieval cashel describes a gentle curve across the grass, the rest of the circuit long since robbed out or collapsed into the agricultural land around it. A cashel is a stone-built ringfort, the western Irish equivalent of an earthen rath, typically enclosing a farmstead or the residence of a person of some local standing. This one, when complete, would have measured roughly 33 metres across.

What survives stands to a height of 1.2 metres and runs to a thickness of 0.7 metres. The construction is uncoursed drystone, meaning the stones were laid without mortar and without the regularised horizontal rows seen in more carefully dressed masonry. The blocks range from fairly substantial, around half a metre long, down to medium-sized pieces, all fitted together by hand and by eye. There is no fosse, the encircling ditch that often accompanies earthen ringforts, which is consistent with a stone-built enclosure of this type. The interior offers nothing visible above ground, though that absence says little about what may survive below the surface. The site sits in good-quality pasture with wide views opening to the south, east, and west, the kind of elevated, well-drained position that early medieval builders consistently favoured when choosing where to settle.