Codex Seraphinianus

Originally published in 1981, is an illustrated encyclopedia of an imaginary world, created by the Italian artist, architect and industrial designer Luigi Serafini in thirty months between 1976 to 1978. The book is approximately 360 pages long (depending on edition), and written in a strange, generally unintelligible alphabet.

The full book is available online here but you can download it, too. (149 MB, PDF)