Beyond the Caves of Chaos (1E)

From publisher blurb: The caves of chaos have been cleansed but an intriguing tunnel was found in the process. Seemingly blocked to bar access, the tunnel plunges deep into the earth. Just inside a black, marble obelisk rests in the middle of the passage. A single rune – the sign of the dread archmage Hilgdred – is the only mark upon the obelisk. Of what concern can the storm wizard have within the deep.