I reall like the idea of the rafters... or anything in the wilderness would be neat, kind of a classic horror film motiff too, which can always be fun.
I guess your system is probably more modern d20, but I've always been a big fan of historical settings.
You could do Roanoke (so that's where everyone went)... or perhaps a western mining town (Donnor Party anyone?)... maybe something during the Civil War (was that the
real reason for Sherman's March to the Sea?)...
And that's just what I've come up with American History at the moment.
M.