I would have to say the strangest book by far was City of Dreaming Books by German author Walter Moers. It’s about sentient dinosaurs who love all things books and knowledge and aspire to be writers. One in particular goes on a journey to the greatest city said to have the rarest books and an adventure ensues.

Walter Moers books are all incredible and strange but not all are translated from German yet. I recommend Rumo as well if you do like his style; same universe different time and protagonists.