A prison built by the Sidhe Ardaithe. In The Wandering Plain, Uaigneach is a room with no escape. The ruins in the material plane, however, have locked doors, trapped entryways, and an orb sealed in a stone casing. Someone has picked the lock and cleared the traps, looking for relics; they seem to have cleaned out the ruins.
Touching the orb teleports a character to The Wandering Plain and vice versa, though it was not usable by those imprisoned by the Sidhe.
It was remote in ages past--in a small forest along the edge of tundra to the north--but Turnbeek has brought civilization too close for comfort.