Man-made underground passage in Keelties

Keelties holds a collapsed underground chamber beneath a rath, marked only by a shallow circular depression and a large firmly set stone in the centre. The passage has vanished, but the stone remains like a plug in a forgotten hole. People may have gone down there to hide, pray, keep something safe or face the dark alone. The chamber is gone, yet the rath still points to the moment the earth opened and swallowed the way down.