There are no markers, no signage, and nothing obvious at field level to suggest that dropping below the surface would bring you into a carefully constructed stone chamber. That chamber, circular and roughly four metres across, rises to a height of about 1.6 metres, its walls formed from dry-laid limestone rubble and its roof built in a corbelled style, meaning the stones are layered inward and upward in overlapping courses until they close together overhead, a technique requiring considerable skill and needing no mortar to hold its shape.

Souterrains are underground stone-built structures found across Ireland, most commonly associated with early medieval settlement, roughly the period between the sixth and twelfth centuries. They were typically connected to nearby habitation sites and are thought to have served as places of refuge, cool storage for dairy produce, or both. The Toberawnaun example follows a pattern seen elsewhere: a primary chamber that then connects to a passage. Here, a lintelled opening at the base of the eastern wall, just 0.4 metres wide and 0.4 metres high, leads into a passage that extends further eastward. That narrow constriction is characteristic of the type; it would slow or stop an intruder while allowing someone familiar with the space to move through quickly.