A sunken, overgrown hollow at the centre of the enclosure marks the roof of a souterrain, an underground stone-lined passage or chamber built by early medieval inhabitants, probably between the seventh and twelfth centuries. These structures are common across Ireland, typically constructed beneath or within ringforts as places of refuge, storage, or concealment. Here, the collapse of the roof has left a tell-tale depression in the ground, nature slowly filling in what once would have been a deliberate void.