A cashel is a stone-walled ringfort, the drystone equivalent of the earthen raths found widely across Ireland, typically enclosing a farmstead or small settlement during the early medieval period. What survives at Cloonnahaha is a roughly circular enclosure measuring approximately 26 metres across its north-west to south-east axis, defined by a wall that has largely collapsed in on itself. The base of that wall still spreads to around five metres in width, though in places the interior face rises no more than thirty centimetres above ground level, and the exterior face reaches just under two metres at its tallest. Unspectacular from a distance, perhaps, but the footprint is legible all the way around.

What gives this modest site a particular point of interest is the souterrain recorded in its western sector. A souterrain is an underground passage or chamber, usually constructed from stone, associated with early medieval settlements across Ireland and Scotland. Their precise function is still debated, though cold storage and refuge are the most commonly accepted explanations. The interior of the cashel itself slopes downward from south-east to north-west, following the natural lie of the hillside, which would have given the original occupants a practical orientation toward drainage while the hill behind offered some shelter from prevailing weather. The collapsed drystone wall, visible as a broad rubble band running the full circuit, gives a reasonable sense of the structure's original extent even in its reduced state.