At Poulbaun in County Clare, a souterrain, an underground stone-lined passage or chamber typically associated with early medieval settlement and used for storage or refuge, was marked on a map in 1977, sitting within the enclosure of a cashel, a dry-stone ringfort. When fieldworkers returned to inspect the site in 1997, they found no trace of it.

The original indication comes from Robinson's map of 1977, which placed the souterrain inside the cashel recorded as CL006-036006. Souterrains are not uncommon features within cashels across Munster; they were dug or built by early medieval farming communities, often connecting to the interior of a dwelling, and they could be concealed, collapsed, or simply overlooked depending on ground conditions and vegetation. Whether the feature at Poulbaun was always difficult to locate, had become obscured in the two decades between the mapping and the inspection, or was perhaps a misidentification on the original map, the 1997 visit produced no confirmation of its existence. It remains on the record as a possibility rather than a certainty, a site defined as much by what could not be found as by what was once thought to be there.