In the south-west quadrant of a ringfort at Ballygirriha in County Cork, the blade opened a small entrance into a souterrain, the term for the stone-lined underground passages and chambers that were built throughout early medieval Ireland, most commonly as places of refuge or cold storage associated with ringfort settlements. What the opening revealed was a carefully constructed passage, its walls formed of fitted stone and its roof covered with flat stone lintels, running for at least 1.3 metres before collapsing into rubble.

What makes the Ballygirriha souterrain particularly interesting is that this 1988 discovery was almost certainly not the first time the ground gave way. Local tradition holds that around 1938, a separate collapse occurred in the south-east quadrant of the same ringfort, and that this earlier event exposed what were described as several rooms. That detail, passed down through local memory rather than formal excavation, suggests the souterrain may have been considerably more extensive than the surviving visible section implies, with multiple chambers extending beneath different parts of the enclosure. The two events, separated by roughly fifty years and different quadrants of the fort, point to a structure of some ambition, most of which now lies beyond reach under compacted earth and fallen stone.