Consider the idea of spontaneous genesis of life, as used to be belived. What strange kinds of life might arise from modern substances? What kind of vermin would a landfill produce, or an oil spill on the ocean?
A demon who isn't some hideous creature bent on consuming souls, bu is, in fact, a likable chap who enjoys having pleasant chats with people - trying to talk them into becoming his servants.
A large river that is continuously covered in a thick layer of fog. There will be either a rope ferry to get across or possibly a boat that is rowed across by worshippers of the water elementals. It is very thick fog to the point where it even muffles voices even at close range and visibility even beyond a foot is almost impossible.