Nothing on the surface confirms it. No earthwork, no hollow, no telltale depression in the ground gives any sign that something lies beneath.

The site is classified as a souterrain, a type of dry-stone underground passage or chamber built during the early medieval period in Ireland, typically used for storage, refuge, or both. What makes this particular example unusual is that the physical structure itself has left no visible trace at all; what survives is purely the memory of it, passed down in local tradition as a cave connected by a tunnel to a fort. The fort in Tirur is a recorded monument in its own right, and the imagined underground link between the two sites speaks to a pattern common in Irish folklore, where souterrains and raths became connected in local memory by rumoured secret passages, often far longer than would have been structurally possible. Whether the Carrownafreevy souterrain ever existed as a built feature, or whether the tradition preserves a distorted memory of separate features once visible in the landscape, is simply not known.