I want to find the absolutely crazy-to-grasp book of all times.
Most articles related to this topic suggest something like the Fight Club. Even though, there are some good twists to the story, I feel like my mind could be blown away way more than that.
Needless to say that we are talking about a book for the HN audience.
Le ton beau de Marot, also by Douglas Hofstadter. Was blown by his description of how making the typographical choice of starting the first word of each chapter with letters decreasing in height to the normal page font size, caused him to rethink a whole chapter (he couldn't use descenders, which limits the first word, which limits his first sentence, which constrains his first paragraph and so on).
Harry Potter and the Methods of Rationality, by Eliezer Yudkowsky. Every single chapter is potentially mind blowing. The whole approach of trying to instruct rationality through such fiction is itself brilliant I think.