A society in which people believe that the hundreds of stars that dot the sky are the dreams of the sleeping. When the sun goes down, and the people of the world rest, the dreams begin to seed the sky, disappearing in the morning as the populace awakes once more. It could be just a folk tale, or it could be real...
A cave with weapons sunken into the walls, blades sticking out of the floor and ceiling, and so on. Possibly, any weapon used in it could be torn out of the hand and sink into the stone.