Measuring roughly 2.4 metres long, 1.8 metres wide, and half a metre deep, it sits about ten metres from the ringfort's bank, and on its north-western edge a single stone slab, a metre long and forty centimetres wide, breaks the surface. That slab is likely the only visible remnant of a souterrain, an underground stone-lined passage or chamber built during the early medieval period, typically beneath or beside a ringfort, and used for storage, refuge, or both.

Ringforts, which are circular enclosures defined by an earthen bank and ditch, were the dominant form of rural settlement in Ireland from roughly the sixth to the twelfth century, and souterrains were a common feature within them. The one at Cloghgriffin belongs to a ringfort recorded separately in the Cork archaeological record. What survives above ground today is the depression left by a collapsed or partially robbed-out structure, the interior having caved in over centuries of disuse and agricultural activity. The exposed slab on the north-western side suggests the original stonework has not entirely disappeared, and that somewhere beneath the subsidence, some trace of the original passage or chamber may remain.