Man-made underground passage in Shangarry

Shangarry is not a ghost story about a woman lost in rock. It is a man-made underground passage, an L-shaped cut inside a rath, with one long chamber running north-south and a shorter chamber leaving its south-west end to run east-west. The interesting part is the shape: a doorway, a turn, and a second room. That is the kind of place where people would have carried fire, hidden things, or moved through darkness without being seen.