Ruins of Undermountain, Rumors Section, pg. 15:
"One of the oldest tales of Undermountain, many still tell of the six Lost Wizards. These wizards, rivals and contemporaries of Halaster, came to the region seeking something from the master of the Underhalls. Tales digress with each telling, many believing the wizards sought knowledge while others say revenge brought them here. Despite these differences, the stories say the wizards now lie dead or imprisoned in Undermountain, their bodies interred with powerful magical items and lost magical knowledge."
Well, we found them! Or, more accurately stated, I placed them - somewhere in Ruins of Undermountain III: The Deadly Levels, with explanatory notes as to who they are and some cool background info!
That material and the associated room/rooms are finished as of a few minutes ago.
