The Turn of the Screw (1898) by Henry James is a classic ambiguous work of psychological and supernatural suspense. The story is open to interpretation and could be viewed as either a true ghost tale or a neurotic hallucination of an unreliable narrator, a mentally unstable governess placed in charge of two remarkable children.
A definite must to read if you like old fashioned ghost stories. It kept me interested the whole time because it's not a predictable story. Very eerie.