What’s the most haunting book you’ve ever read?

I don’t mean just scary or unsettling… I’m talking about the kind of book that lingers in your mind for days, maybe even years. The one that seeps into your thoughts at random moments, like a memory you can’t shake.

For some people, it might be a classic horror story. For others, maybe it’s a quiet novel with themes of loss, loneliness, or existential dread…

So, what’s the most haunting book you’ve ever read ? and why did it stay with you?