A souterrain is an underground passage or chamber, typically built during the early medieval period, often associated with the ringforts and enclosures that dot the Irish countryside. They served variously as places of refuge, storage, or escape routes. This one, if it exists at all, has been closed up for so long that the ground above it gives nothing away.

What is known comes from local tradition rather than excavation or survey. The rath at Greenane, a type of circular earthwork enclosure common across Ireland from roughly the sixth to the twelfth centuries, is recorded as containing a souterrain according to information passed down within the community. No archaeological investigation appears to have confirmed or disproved it. That ambiguity is itself revealing: a great many souterrains across Ireland were blocked or collapsed long before any systematic effort was made to record them, and oral memory sometimes preserves knowledge of features that are invisible at ground level. Whether this is such a case, or whether the tradition refers to something that never existed or has since been confused with another site, remains an open question.