The ground simply collapsed, and what emerged was a souterrain, an underground chamber or tunnel constructed from stone, typically associated with early medieval settlement in Ireland and used variously for storage, refuge, or both. This one is orientated north to south and sits on a south-facing slope of pasture, roughly eighty metres northwest of Belanagare well.

Souterrains are not especially rare in County Cork, but the manner of this one's discovery gives it a particular quality. It was not found through systematic excavation or aerial survey but through the ordinary violence of agriculture, the land yielding under pressure what centuries of quiet had kept hidden. The proximity to Belanagare well is worth noting. Holy wells in Ireland frequently mark early Christian or pre-Christian places of significance, and their presence in a landscape often clusters with other early medieval features, suggesting that the immediate area around Rahan may have supported a small community or settlement at some point before the Norman period.