Chronicles of the Splintered Realm Volume 1: The Abyssal Labyrinth

From the introduction:

I have long wished to create an ‘ultimate’ dungeon crawl, feeling that each great fantasy world is, in many ways, defined by its great dungeon. Greyhawk grew out of the ruins of Castle Greyhawk; The Forgotten Realms has been shaped by Undermountain; Middle Earth by Moria; Star Wars by the Death Star (if you want to stretch).
...
While several of the dungeons in Dark Age of Camelot fired the imagination, my favorite over the time I played was a huge complex called Darkness Falls, a conduit into the hells filled with demonic creatures and terrible horrors. Some of my favorite game moments were spent crawling through Darkness Falls.

The Abyssal Labyrinth is my answer to DF[.]