Suggest me a horror/scifi book with a monster that gave you nightmares?

Looking for a book (horror/scifi) with a creature that was written so well that it terrified you. One that made you nervous for the main characters, could be a good or bad ending, as long as it's written well.

Doesn't have to be sci-fi either, but the feeling i'm looking for is like in Alien: Isolation with all those tense moments with the alien when the player is hiding.