I seem to remember there was a project done by somebody in the OSR where they finished detailing the underdark map found in the D series. For the life of me I can remember where it is. Does anybody know what I am talking about? I think I found it a 1 1/2 to 2 years ago.
Thanks to James and Mr. Castle I found it here the Encyclopaedia Subterranica and the corresponding Dragonsfoot thread.
What I liked about this project was that it filled in the rest of the map from the D series. While I was never really into the underdark for my campaign I hate unknown spaces on maps. I just want to know what there. Thanks to the Dragonsfoot team now we have a version that fills in the unknown.