That single annotation, appearing on the 1933 edition of the OS 6-inch map, is now the only surviving evidence that a souterrain once existed within the rath at Gortymadden. A souterrain is a man-made underground passage or chamber, typically stone-lined, associated with early medieval settlement in Ireland. They were built beneath or alongside raths, the circular earthen enclosures that served as farmsteads, and are thought to have functioned as places of refuge, cool storage, or both. At Gortymadden, no trace of the structure remains visible at the surface.

The rath itself still exists as a recorded feature, but the underground component has effectively vanished, leaving behind only its cartographic ghost. The 1933 OS map captured something that was presumably still identifiable to surveyors at that time, or at least present in local knowledge, but whatever opening or depression once marked the souterrain's presence has since been lost, filled in, or simply obscured by time and agricultural activity. It is a common enough fate. Souterrains across Ireland have been collapsed, built over, or quietly forgotten as the landscapes around them changed use across the centuries. What makes this particular case quietly striking is how completely it has disappeared, not just from the ground but from any later record, leaving the 1933 annotation as the sole witness.