The label refers to a souterrain, an underground stone-lined passage or chamber typically associated with early medieval ringforts, used variously for storage, refuge, or ventilation of adjacent structures. The word survived on the maps for nearly a century. The souterrain itself did not.

The rath, a circular earthwork enclosure of the kind built across Ireland during the early medieval period, contains within its western half the ghost of this feature. At some point after 1931, three quarry pits were cut into that western portion, removing the ground to depths of between 0.6 and 1.8 metres across areas measuring up to roughly five by ten metres each. The digging was extensive enough to obliterate whatever underground structure had once warranted a name on the map. No trace of the souterrain remains. What survives is the documentary evidence of its existence and the absence where it once was, a gap in the archaeology that the landscape offers no clue to without the older maps to consult.