A souterrain is a dry-stone underground structure, typically associated with early medieval settlement, used variously for storage, refuge, or concealment. What makes this one quietly arresting is not just its age but its internal logic: a network of passages and chambers arranged at right angles to one another, some now collapsed, some flooded, and at least one portion extending beyond a carefully cut port-hole at ground level, small enough that a person would have to press flat to pass through it. That opening measures just 48 centimetres wide and 33 centimetres high, and whoever shaped it did so with some precision.

The structure begins with a present-day entrance set back four to five metres from the edge of the scarp, opening into a passage that runs roughly 1.5 metres to the north-east before meeting a second passage running at right angles. That second passage reaches no more than 85 centimetres in height and between 60 centimetres and a metre in width; its full length was never established. Around four metres from the entrance, collapsed roofing slabs block the north-western end, though a further end wall appears to exist some six metres beyond the collapse, with a gap that may indicate yet another chamber. At the south-eastern end of the passage, a single slab forms a wall, and it is here that the port-hole was cut, leading to a flooded chamber with a curved end wall and a further possible passage beyond. A piece of pottery was apparently recovered from within the souterrain, noted by O'Sullivan in 1931, though no further detail about the find was recorded. The site was documented in detail by J. Cuppage in the 1986 Dingle Peninsula archaeological survey.