The Voynich Manuscript
This story got my attention a while back. I'm not sure what to think of it. I've seen a lot of strange things, but nothing like this. No one knows in what language it was written. The illustrations sometimes show plants with animal shaped root systems and there are lots of images of females bathing in very complex systems pf plumbing. It dates to the early 15th century; some even think it's a hoax.
Click photo for the Wikipedia link.
The Codex Seraphinianus is a modern book that is also very interesting, and expensive.