Shadows of the Dread Spiral (2006)

A one-Round Living Greyhawk Core Special Adventure

From the introduction:

A tainted soul seeking redemption draws your attentions to the foreboding Yatil Mountains. Within its hidden recesses lies the Forgotten Temple of Tharizdun, and there, a terrible labor lost in time begins anew, as the veil between worlds grows thin, and a threat more perilous than all others reaches out to touch the other side.

This adventure is divided up into two levels of play (low level and high level); each player may only participate in one of them.

A challenging special adventure for characters levels 1 - 15.