I was thinking about running Dark Souls atmospheric game set in Greyhawk. The characters wouldn't be undead, but the area would be dark, filled with monsters and undead. I would probably run this with one player, who would be a follower of either Pelor or Pholtus. I'd probably make a new class, similar to the Paladin, but with no holy mounts and more fire-based magic.
In any case, is there a region that would fit easily for this? I'm thinking of either the Hellfurnaces west of the Sea Princes, or somewhere around Iuz. Any suggestions?