Yet beneath this diminished caher, a cashel being a type of stone ringfort enclosed by a dry-stone wall rather than an earthen bank, something more intact persists. Tucked into the southern bank is the entrance to a souterrain, an underground passage and chamber system of the kind commonly associated with early medieval settlement in Ireland, used for storage, refuge, or both. The opening is small, roughly three-quarters of a metre across, and the passage beyond it runs northward for just over three metres, lined with earth on either side and roofed with stone lintels. Near the entrance, a single upright slab is wedged between two of those lintels and hangs down into the passage, an odd, almost deliberate-looking obstruction whose precise function is not entirely clear.

The caher sits on rough pasture on the lower south-western slopes of Cahernageeha mountain, in the area of Doire Fhionáin Beag in County Kerry, looking out over Darrynane Bay to the south. The souterrain's inner arrangement is more complex than the modest entrance suggests. Past the main passage, a creepway, a low tunnelled crawlspace, opens off the western side of the northern end and leads into a larger sub-rectangular earth-tunnelled chamber. A second creepway was noted on the western side of that chamber, though it could not be investigated at the time of survey due to flooding. The structural sequence, passage giving way to creepway giving way to chamber, is fairly typical of Kerry souterrains, where the awkward transitions between sections may have served as a practical deterrent to anyone entering without invitation. The caher's internal measurements, about 12.8 metres north to south and 14.4 metres east to west, suggest a modest enclosure, probably associated with a single farming household rather than any kind of larger settlement. The whole complex was documented by Aidan O'Sullivan and John Sheehan in their 1996 archaeological survey of the Iveragh Peninsula, published by Cork University Press.