Man-made underground passage in Killynure (castlerahan By.)

Killynure rath in County Cavan holds a waterlogged depression eight metres long inside its western bank, perhaps marking a forgotten underground passage. The shape is clear enough to suggest deliberate construction rather than casual collapse, yet the missing structure leaves the function open to imagination. Someone cut through solid earth, created a narrow chamber and abandoned it to rain and time. The rath still stands around that hollow, waiting for the lost passage to reappear in memory or excavation.