The two I can think of are below, but knowing such a thing about either one is a major spoiler for them both, as it’s not entirely clear as you read what the deal is. Both are quite strange books and often make the lists when people ask for “weirdest of all time” books.

>!The Third Policeman by Flann O’Brien!<

And

>!The Unlimited Dream Company by J. G. Ballard!<