The opening is modest, less than a metre wide, and the darkness beyond it belongs to an early medieval souterrain, one of the many underground stone-and-earth structures built across Ireland, typically associated with ringforts and cashels, and thought to have served as refuges, cool storage spaces, or both. What makes this particular example quietly compelling is the detail preserved in its description: a lintelled passage barely wide enough for an adult, its walls of compacted earth rather than stone, extending roughly 3.3 metres northward before arriving at something stranger.

Close to the entrance, a single vertically placed slab hangs down from between two roofing lintels into the passage itself. Whether this acted as a baffle to slow an intruder, to trap smoke, or served some other now-forgotten purpose is not recorded, but its deliberate placement is hard to read as accidental. At the far end of the passage, a creepway, a narrow crawl-through tunnel, leads west into a larger sub-rectangular chamber hollowed from the earth. A second creepway was identified on the west side of that chamber, though when surveyed it was inaccessible due to flooding, leaving whatever lies beyond it unrecorded. The caher, a dry-stone cashel or ringfort of the kind common across the Iveragh Peninsula, provided the structural context for all of this, its southern bank forming the very wall through which the souterrain's entrance was cut. The structure is documented in A. O'Sullivan and J. Sheehan's archaeological survey of the Iveragh Peninsula, published by Cork University Press in 1996.