Beneath or somewhere near a field in County Galway, there may be a souterrain, an underground stone-lined passage or chamber typically associated with early medieval settlement, used variously for storage, refuge, or both. The operative word is "may": the feature was never excavated, never confirmed, and the landscape that might have helped locate it has long since been erased.

The trail begins with a 1912 observation by a researcher named Holt, who recorded a low mound lying to the west of the centre of the garth, meaning the enclosed yard or ground associated with a rath, and suggested it probably marked a souterrain below. A rath is a roughly circular earthen enclosure, common across early medieval Ireland, typically surrounding a farmstead. The particular rath at Ballynacourty has since been levelled entirely, taking with it any surface evidence of the mound Holt described. Whether the souterrain itself survives underground, undisturbed beneath the soil, is simply not known. No subsequent investigation appears to have settled the question either way.

What remains, then, is a note in the record, a single cautious sentence from 1912, pointing at something that may still exist in the dark below a field that gives no sign of it whatsoever.