A souterrain is an underground stone-lined passage or chamber, typically built during the early medieval period, used for storage, refuge, or both. This one is known only through a single line in an older record, and the ground above it gives nothing away.

In 1934, a researcher named Bowman noted the "site of Souterrain on N. of rampart" within the ringfort at Gortearagh. A ringfort, to clarify, is a roughly circular enclosure defined by earthen banks and ditches, the most common monument type surviving in the Irish countryside, and the great majority date to the first millennium AD. The souterrain Bowman recorded would have been ancillary to whatever settlement once occupied this enclosure. By the time the site was catalogued more formally, no visible surface trace remained. Whether the passage collapsed, was filled in, or simply became indistinguishable from the surrounding ground is not recorded. What survives is essentially the memory of an absence, a note that something was once observed to have existed, without any detail of what was seen or how it appeared.