The heroes find the crumbling, overgrown ruins of what appears to be some sort of grand dining hall in the forest. Deciding that it is a good place to camp, the set up a fire in the center. However, they are woken in the night to see skeletons waltzing in the moonlight to organ music that emanates from the open air. The skeletons touch nobody, dancing around them all night.
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.