The opening measures just 45 centimetres high, barely enough to squeeze through, and beyond it lies a carefully constructed underground passage that dips, levels off, and rises again before meeting solid rock. This is a souterrain, an artificially built underground structure typically associated with Irish ringforts and cashels, used variously for storage, refuge, or concealment. What makes this one quietly unusual is what happens at the far end: beneath the rock-face at the northern terminus, a natural passage continues downward at a steep 45-degree angle, leading to what is likely a chamber beyond.

The souterrain sits within a cashel, a type of stone-walled enclosure used as a farmstead or defended homestead during the early medieval period in Ireland. It is positioned in the north-east centre of that enclosure, occupying its lowest ground. The passage runs roughly north-north-east to south-south-west, extending 3.35 metres in length and a metre in width. Seven stone lintels roof it along its course, a construction method typical of Irish souterrains, where large flat stones are laid across the side walls to form a ceiling. The passage descends after entry, reaches a maximum internal height of 1.3 metres at its most generous point, then narrows and rises again to just 0.9 metres before the rock-face. The transition from built structure to natural fissure at the northern end, where human construction gives way to geology, adds a layer of ambiguity to the site's original purpose and extent.