Man-made underground passage in Maulnaskeha

Maulnaskeha ringfort in County Cork, Ireland hides a man-made underground passage beneath its western bank. The entrance has vanished into a depression in the earth, but the shape of that hollow still betrays the tunnel below. People may have dug it to store grain, escape storm water or reach another part of the fort without crossing open ground. Whatever they intended, the passage turned a ordinary ringfort into a place where the ground itself could swallow a person and return them elsewhere.