A cashel is a type of early medieval ringfort enclosed by a drystone wall rather than an earthen bank, and this one measures roughly 25 metres in diameter. What makes the site curious is how much of that wall has simply melted into the ground. From the south-west around through the north and across to the east, the enclosure survives only as a spread of loose stone; elsewhere, a later field wall has been pressed into service to complete the circuit, blurring the boundary between ancient monument and working landscape.

Associated with the cashel are the remains of a number of houses, suggesting that this was once a settled domestic enclosure of the kind that dotted the Irish countryside throughout the early medieval period and beyond. Cashels of this type were typically the homesteads of farming families, the drystone wall serving both as a boundary marker and as a modest defensive barrier for livestock. The Keernaun example has not fared well against time and agricultural reuse, but the outline endures, and the scatter of associated structures gives a sense of a small community that once organised its daily life within and around these stones.