I've finally got something resembling an idea. It's inspired somewhat by Pitch Black, the movie with Vin Diesel. Firmly not a fanfic, though!
Here's the general synopsis:
An innocent, naive priest/cleric type has been given a vision... she must go into the dangerous no-man's land to retrieve some object of great power and divine significance. It's a dangerous place, full of convicts, rogue mages, dangerous creatures, and all manner of indescribable beasts and challenges. The only problem is that there's only one person who's ever been known to enter that place and return alive. And he's a convict. A very nasty one, at that. He was exiled to the no-man's land (to be named) for an unspeakable crime, but managed to find his way back.
Now, that vision demands that she take him, and only him, into that place if she has any hope of survival, much less success. She will find allies in that place, but if he does not enter and return with her, then she will not recover the artifact, and will probably die. The vision's pretty specific.
The clergy officials verify her dream, as it agrees with visions that have been reported by seers and other clergy. So she must go to the deepest dungeons to retrieve this convict, somehow convince him not to kill her as soon as they leave the safety of the church. I'm thinking geas, of the sort that binds him to her. If she dies, he dies, sort of thing. The promise of a full pardon and release from the geas is his reward for returning safely with her.
They leave on their journey, and much adventure follows.