That modest cartographic notation is, in all likelihood, the most visible this structure has ever been, because today nothing at ground level survives to mark it.

What the mapmakers recorded was a souterrain, an underground stone-lined passage or chamber, typically constructed during the early medieval period as a place of refuge, storage, or cool keeping for perishables. This particular example sat within the eastern half of an enclosure, a ringfort or similar bounded settlement of the kind once scattered densely across the Irish countryside. The enclosure itself survives as a separate recorded site. The souterrain does not. Somewhere beneath the field, the passage may still exist in some form, but the surface trace has been lost entirely, leaving only the old map annotation as evidence that people once knew it was there and thought it worth naming.