A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval settlement in Ireland, used variously for storage, refuge, or both. The one at Tullig is recorded, catalogued, and assigned a reference number, yet the ground above it offers no visible clue that anything lies beneath.

The site entered the record in 1927, when a researcher named Ua Riain noted what appeared to be a souterrain here. The phrasing is careful: possible. Whether the structure was partially visible at that point, or inferred from some surface depression or local knowledge, is not clear. What is clear is that by the time attention returned to this corner of the Iveragh Peninsula in more recent decades, nothing remained on the surface to confirm or locate it. The land has, in effect, closed over the question entirely.