It may be a souterrain, one of those narrow underground passages built in early medieval Ireland, typically as storage chambers or places of refuge, roofed with flat lintels and entered through a low doorway. Or it may simply be the ruins of a sheep-shelter. The uncertainty is part of what makes it interesting.

The scholar R.A.S. Macalister noted the souterrain in 1899, describing it as more than six feet long with a well-built door, though it was not accessible at the time of his visit. When the Dingle Peninsula Archaeological Survey, published by J. Cuppage in 1986, returned to the area, the remains it found sat not in the southern corner of the field where Macalister had placed it, but in the centre, among a wider cluster of monuments. What survives is a structure formed by two parallel lines of walling running roughly east-south-east to west-north-west across the slope, at least two metres long and about seventy centimetres apart. The north-east side is built of drystone masonry, standing to around seventy-five centimetres; the south-west side is defined by a single upright slab and a run of collapsed stones. The eastern end is closed off by a single course of drystone walling, while the western end is open and may once have continued further. Several flat slabs lie scattered inside and outside the structure, and these could be the remains of a lintelled roof, the kind of covering that would be expected of a souterrain. Whether the structure matches what Macalister saw, or whether he was looking at something else entirely, is not resolved.