Pillow-Problems by C.L. Dodgson. Maybe you might not be familiar with the name, but reading this book takes you deep into the rabbit hole. Of course Charles Lutwidge Dodgson was the real name of Lewis Carroll, the author of classics like Alice in Wonderland and Through the Looking Glass. Not many people know he also lectured in Math in Christ Church College in Oxford. His Pillow Problems were puzzles he came up with before falling asleep, hence the title.
You can read them here (link); for a moment I really thought that it said ‘Fart II’ on the cover, but a dirty mind… etc.