The entrance, it was noted in the 1980s, had been closed up for many years even then, and today there is nothing visible at the surface to suggest the feature exists at all. That combination, a probable souterrain sealed off within a ringfort, is precisely the kind of quietly unresolved detail that makes a place worth pausing over.

A souterrain is an artificial underground chamber or passage, typically drystone-built, associated with early medieval settlement in Ireland and often found inside or close to a rath. A rath, sometimes called a ringfort, is a roughly circular enclosed farmstead dating broadly to the first millennium AD, defined by one or more earthen banks. They are among the most common field monuments in Ireland, yet each conceals its own particular history. At Killeagh, the rath in question was surveyed as part of the Castleisland District Archaeological Survey, which recorded the tradition of a large cave beneath it. Whether that cave is a true souterrain constructed by human hands, or a natural formation that was later incorporated into the site's use, remains unclear. No physical remains are now visible, and the entrance has apparently been blocked for so long that even the 1980s record could only speak of it in the past tense.