That absence is part of what makes it interesting. A souterrain, to give it its proper name, is an artificially constructed underground passage or chamber, typically associated with early medieval settlement in Ireland, often interpreted as a place of refuge, storage, or concealment. This one is accessed through a modern opening, but what lies beyond is considerably older in character.

The structure runs broadly east to west, beginning with a lintelled passage whose walls are of earth rather than stone, measuring at least 2.7 metres in length and just 0.6 metres wide. The western end has narrowed and collapsed. Moving eastward, a low creepway, only 0.75 metres high, connects the passage to the first of two tunnelled chambers, roughly rectangular in plan, measuring around 2.45 metres by 1.7 metres, with a roof just a metre above a floor partly buried in fallen earth. A second, similarly proportioned chamber lies beyond another creepway, even lower at 0.4 metres, requiring a person to crawl almost flat to pass through. Both chambers share a detail of particular interest: patches of drystone facing, each about 0.8 metres long, positioned at the points where the chambers adjoin their connecting creepways. These are thought to represent the blocked-off construction shafts through which the chambers were originally excavated from above, the builders tunnelling outward from a central point and then sealing the evidence of their method behind dressed stonework once the digging was done. It is a glimpse of early medieval engineering logic, modest in scale but precise in intent.