What makes it quietly odd is not the structure itself but what someone added to it: roughly two and a half metres inside the entrance, a well was dug into the passage floor. A souterrain, that is an underground stone-built tunnel associated with early medieval ringforts and used variously for storage, refuge, or ventilation, would not typically need its own water source. The combination hints at purposes that are not immediately obvious.

The souterrain sits within a rath, the Irish term for a circular earthen enclosure of the early medieval period, which still survives at the site. When archaeologists first inspected the passage in April 1983, they entered from the southeast end and found a drystone-built structure standing 1.65 metres high, its width shifting from one metre at the entrance to 2.2 metres at the mid-point before closing to just 0.6 metres at the far wall. Stone-facing visible just beyond the access point, extending about 1.8 metres further, suggested the tunnel may originally have continued beyond what was then accessible. A reference in McCaffrey's 1952 catalogue places the site within an older tradition of recorded monuments in the area.

By October 2001, when the site was revisited, the entrance had been partly blocked with timber to stop livestock from falling in. A sloe bush had begun to grow across the opening. The passage had not disappeared, but it had begun to be absorbed back into the ordinary life of the land around it.