About twenty metres from a nearby house, the machine struck the edge of an underground network of passages and chambers that had sat undisturbed, more or less, beneath the hillside overlooking Bantry Bay. It was an accidental discovery of the kind that occasionally reminds people how much early medieval Ireland lies just beneath the surface of ordinary farmland.

A souterrain is an underground structure, typically earth-cut or stone-lined, associated with early medieval settlement in Ireland, most likely used for food storage, refuge, or both. What archaeologist Eamonn Cotter recorded at Crooha Middle was a notably complex example. From the southern end of the excavated pit, an opening led eastward into a chamber roughly 3.2 metres long; near its far end, a creepway, just 0.54 metres wide and 0.7 metres high, tight enough to require crawling, opened into a small subcircular chamber whose southern end had been sealed with drystone-walling. On the western side of the pit, a separate opening led into a passage extending about two metres before it was blocked by collapsed or back-filled stone and earth. South of that passage, a further low and narrow opening gave onto two additional passages running south and west respectively. The entire system is earth-cut, with no surviving stone lining to the walls. The landowner had already turned up three large flat stones, each approximately 1.5 metres long, which are thought to have been roof-slabs, possibly from an original entrance. Signs of earlier disturbance were also present: a sherd of modern earthenware pottery and fragments of mud plaster had found their way inside at some point before 1991, suggesting the souterrain had been at least partially accessible in more recent centuries without anyone formally recording its existence.