What emerged was a souterrain, a type of man-made underground passage and chamber system built in drystone masonry, typically associated with ringforts across early medieval Ireland and used variously for storage, refuge, or both. The structure here is L-shaped in plan and comprises three chambers connected by low, narrow creepways that would require anyone moving through them to crouch or crawl. The ringfort above it remains only probable rather than confirmed; its existence is suggested by a distinct curve in an east-west field bank that overlies part of the souterrain, the earthwork of the original enclosure having been absorbed, over centuries, into the working field system.

The souterrain was inspected by Kelly shortly after its discovery and described in detail in J. Cuppage's 1986 archaeological survey of the Dingle Peninsula, Corca Dhuibhne. The three chambers are arranged in a sequence of decreasing size and increasing ingenuity. The first is a large rectangular space, roughly 3.1 metres long and up to 1.72 metres high, with slightly corbelled drystone walls narrowing toward the roof slabs. A porthole slab, an opening cut through a standing stone to allow passage while restricting it, connects this chamber via a tight creepway to the second, which is similarly rectangular and aligned on a roughly east-west axis. A curving passage then leads from the second chamber to the third, meeting it at roughly 45 degrees. That third chamber is entirely different in character: a tiny beehive-shaped space just one metre in diameter and 0.7 metres high, constructed of corbelled masonry set on a foundation course of upright slabs and roofed by a single large slab. The original entrance to the whole system was through the roof of the linking passage between the second and third chambers, where large jamb stones are still visible on either side.