A souterrain is an underground stone-built passage or chamber, typically constructed during the early medieval period in Ireland as a place of refuge, cool storage, or concealment. At Carrigboy, the chamber itself has not been formally excavated or documented from direct inspection; its existence rests on local information and the tell-tale hollow in the earth above it.

Ringforts, the circular enclosed settlements that dot the Irish countryside in their thousands, frequently incorporated souterrains as a practical feature of domestic life. The association here places this underground space within a wider pattern of early medieval settlement, where communities built both above and below ground in the same enclosed farmstead. The Carrigboy example sits in the north-western quadrant of its parent ringfort, a positioning that is not unusual, though the precise date of either feature has not been established from the available evidence.