What remains visible above ground is a collapsed opening that hints at the scale of what lies below: a corbelled chamber, its walls built from carefully placed stones that lean inward to form a self-supporting roof, sealed overhead with large flat slabs. The structure is inaccessible, which means its condition, extent, and original purpose remain matters of inference rather than direct examination.

The feature is a souterrain, an underground stone-built passage or chamber found across early medieval Ireland, typically associated with ringforts. Ringforts, the most common archaeological monument type in Ireland, were enclosed farmsteads of the early medieval period, surrounded by one or more circular earthen banks or stone walls. Souterrains were built within or beneath them, and are generally understood to have served as refuges, cool storage spaces for dairy produce, or both. The Garranereagh example sits at the centre of its associated ringfort, a placement that is not unusual, though the collapse of its entrance means the relationship between the two structures can no longer be easily read on the ground. The corbelled construction technique, in which no mortar is used and each course of stone projects slightly inward until the walls meet, is a method with deep roots in Irish building tradition, appearing in monuments ranging from Bronze Age tombs to early Christian beehive cells.