How about in a normal village that gets consumed by a demonic darkness where the darkness in people's hearts takes phsysical form and emerges from their owner's shadows to devour them. If you commit any remotely dark or evil act the darkness form your own heart devours you. The adventurers would have to escape the village while possibly helping out the survivors to keep themselves from accumulating darkness within their own hearts before they themselves are devoured.
I had a dream like this once and words cannot describe how terrifying it was. I'm putting this in a book I'm writing and it's pretty freaky.
Besides nothing scares adventurers more than something they cannot fight or run from. After all, who can run from their own shadow?