Built into that face is a blocked entrance to an underground passage that does not appear on Ordnance Survey maps, which gives some sense of how quietly this structure has persisted. A souterrain, for those unfamiliar with the term, is an artificially constructed underground passage or chamber, typically associated with early medieval settlement in Ireland and thought to have served as storage space, a refuge, or both. This one, despite its anonymity on the official record, is a carefully made thing.

The platform itself measures 11.5 metres square, and a second opening on its southern side allows entry into a passage running east to west, roughly 2.5 metres long, less than a metre high, and just over a metre wide. Midway along the northern wall of this passage, a lintelled creepway, a low connecting opening only 55 centimetres square, leads into a second passage extending northward. Collapse has blocked further progress along it, but the presence of a sealed opening at the northern face of the platform suggests this second arm may originally have run to around nine metres in length. The construction throughout is precise: flat slabs laid in regular courses, with large lintels capping both passages. The drystone technique, using carefully fitted stone without mortar, is consistent with early medieval practice across the Iveragh Peninsula, a landscape that the archaeological survey compiled by A. O'Sullivan and J. Sheehan in 1996 revealed to be extraordinarily dense with early settlement remains. That the souterrain was built on a raised platform, oriented to overlook a coastal channel, adds a layer of deliberateness to its siting that is not fully explained by simple agricultural storage.