It does not look like much on the surface, but it marks the collapsed roof of a souterrain, an underground stone-lined passage or chamber built by early medieval inhabitants, typically used for storage, refuge, or both. These structures are fairly common on ringfort sites across Ireland, but they are rarely so precisely described or so visibly intact as an open depression.

The earliest recorded account of this particular feature comes from Bowman, writing in 1934, who identified the hollow as the remains of a souterrain within the inner rampart of the fort. McCarthy noted it again in 1977, and the visible cavity has persisted since at least that first observation. What makes the site quietly interesting is not just the souterrain itself but the suggestion of a second one in the adjoining field, recorded as a possible example, which raises the question of whether this was a more extensively modified landscape than the single ringfort implies. Two souterrains in close proximity, if both are confirmed, would point to a settlement of some complexity and duration.