The site is recorded on the basis of local tradition alone, which holds that a cave or souterrain lies to the west of centre within a ringfort. A souterrain is an artificially constructed underground chamber or tunnel, typically built during the early medieval period and associated with ringforts across Ireland, most likely serving as storage space, a refuge, or both. At Cappagh, there is no visible trace of it at ground level.

The ringfort itself is a documented site, a roughly circular enclosure of the kind that once served as a farmstead in early medieval Ireland, defined by earthen banks or stone walls and occupied by a single family or small community. Whether the souterrain tradition at Cappagh reflects a genuine buried structure, a long-collapsed feature, or a memory of something seen and then lost, is not recorded. What survives is the oral knowledge that something once existed underfoot, passed down through local communities and eventually set down as a formal note against the site. That kind of transmission is itself a small piece of social history, evidence that people noticed, remembered, and kept talking about what lay beneath their land even after the ground closed over it entirely.