Goeffrey McKinney used the obscure the old Ambroise Bierce story Carcosa as the basis for a truly unique and horrific setting for fantasy roleplaying games. I came across this scan from an old copy of Weird Tales, the classic fantasy/horror pulp. It would be fun to create a game setting out of it:
I'd never heard of the author, R. Jere Black, Jr., but it seems he was a rather interesting fellow. I'm also impressed with the art included here. A little research reveals it to be Hugh Rankin, who illustrated many of the early Robert E. Howard stories, and who created some of the first images of Conan.