A cashel is simply a stone-walled ringfort, the kind of enclosed farmstead that thousands of early medieval Irish families built to protect their households and livestock, typically between the sixth and tenth centuries. What makes this one quietly interesting is not its condition, which is poor, but what lies beneath it.

Associated with the enclosure is a souterrain, an underground stone-lined passage or chamber of the kind commonly built in early medieval Ireland as a place of concealment, cool storage, or emergency refuge. Their entrances are often difficult to locate, and their interiors can be cramped and low. The cashel at Cahergalloon was noted by McCaffrey in 1952, appearing in his catalogue at number 68, suggesting that even in its ruined state it was considered worth recording as part of the broader pattern of early settlement across County Galway. The pairing of a cashel with a souterrain is not unusual; the two features frequently occur together, the underground passage serving the needs of whoever lived within the enclosure above.