The ringfort at Istalea sits on a gentle rise above the valley of the Cummeenboy stream, and while it reads at a glance as a grassy mound in pasture, its interior conceals a souterrain, an artificially constructed underground passage or chamber typically built during the early medieval period, probably used for storage, refuge, or both. That combination, an earthen enclosure with a hidden subterranean component, makes this a more layered site than its unassuming appearance would suggest.

The rath itself is broadly circular, measuring roughly 37.5 metres east to west and 37 metres north to south, and is defined by an earthen bank that stands considerably more prominent on its exterior than its interior, with an external height of around 1.55 metres against an internal height of just 0.4 metres. To the north-east, the outer face of the bank has been cut back to create an almost vertical profile, possibly through agricultural activity over the centuries. Cattle-breaks, gaps worn into the bank by livestock, are visible at the north-east and south-west. An external fosse, a defensive ditch running around the outside of the bank, survives to the north and north-east, though it is shallow by medieval standards at around 0.4 metres deep. The interior sits slightly raised above the surrounding ground level and slopes gently down toward the north-east, its surface now heavily overgrown. Ringforts of this type were the commonest form of rural settlement in early medieval Ireland, typically enclosing a farmstead and its associated buildings, and this example in south-west Kerry fits comfortably within that tradition while retaining the added curiosity of its underground feature.