Souterrains are the stone-lined underground passages and chambers found throughout early medieval Ireland, typically built beneath or beside ringforts and used for storage, refuge, or both. The one at Raheens in County Cork ticks most of the formal boxes: a narrow entrance passage, a creepway, a chamber, a secondary passage leading off from it. But when archaeologists examined it, they found no evidence of collapsed stone lining or roofing, and the whole structure had been backfilled with domestic debris. The working conclusion is that it may have been abandoned, or perhaps altered, before it was ever put to use.

The site came to light in 1989, when archaeologist Anne-Marie Lennon excavated it ahead of partial destruction by the Sandoz factory nearby. It sits within a ringfort, the circular enclosed farmstead that was the dominant form of rural settlement in early medieval Ireland, and the souterrain-like structure lies atop several earlier features, suggesting the ground here had already seen repeated occupation before anyone attempted to dig passages into it. The dimensions recorded are modest, as these things go: the creepway running north-northwest measures roughly 2.5 metres long and less than a metre high, tight enough to require crawling, while the possible chamber beyond it reaches about 2.6 metres in length and 1.5 metres in depth. A second, shorter passage continues northward from the chamber. Whether the builders ran out of intention, material, or time is not recorded.