Man-made underground passage in Lisnagry

Thirty feet of hollow earth hide inside the Lisnagry rath, bending like a buried tongue before disappearing under the grass. The chamber is wide enough for two people to walk side by side, yet shallow enough that a jumping child might break through the roof. Build that much deliberate space beneath a ancient fort and you are not digging a drain; you are making a room for secrets, panic or ceremony. The earth forgot the purpose but never erased the shape.