What emerged was a souterrain, an underground stone-built passage and chamber system of the kind constructed throughout early medieval Ireland, typically for storage, refuge, or concealment. What made this particular example worth recording was its plan: not a simple corridor, but a T-shape formed by two chambers meeting at right angles.

McCarthy, writing in 1977, described the layout in some detail. The first chamber runs on an east-west axis, with its western end cut into clay. A creepway, a low connecting passage through which a person would have to crouch or crawl, leads from the centre of the northern wall into the second chamber. The entrance to this creepway is framed by upright jamb stones, a small but deliberate architectural touch. Both chambers are roughly similar in size, each averaging about five metres in length, 1.3 metres in width, and 1.8 metres in height; large enough to stand upright in, narrow enough to feel entirely enclosed. The roofing throughout, including the creepway, consists of flat stone lintels laid across the walls, a method that has kept these structures intact underground for over a millennium in many parts of Ireland.