This narrator's statement is an example of _________.
"I read that every known superstition in the world is gathered into the horseshoe of the Carpathians, as if it were the centre of some sort of imaginative whirlpool; if so my stay may be very interesting, (Mem., I must ask the Count all about them.)"

Foreshadowing means hinting at something that is going to happen later in the plot. In this case, when the narrator comments that the area he is traveling to is known for superstitions and that his stay may be "very interesting," the reader gets the sense that something unexpected is going to happen later on. Allusion is a reference to someone or something well-known or famous that the reader can make a connection with and that's not happening here. Personification means giving human qualities to nonhuman things, which also isn't present in this sentence. Understatement is usually created by sarcasm or irony to point out something obvious. That is not happening in this sentence, either.