What book do you think about on a daily basis?

I'm not looking for selfhelp books. But what sci-fi, fantasy, romance, horror whatever genre. What book keeps you up at night? What book has you in a chokehold? What book do you think about on the daily? I need more of those books.

Mine is Cloud Cuckoo Land by Anthony Doerr. I read it 2 years ago and am still not over it.