I'm pretty sure that if I could take one book with me to a desert island, it would be this one - and all the writing in it is completely unintelligible. From the Wikipedia entry:
The Codex Seraphinianus is a book written and illustrated by the Italian artist, architect and industrial designer Luigi Serafini during thirty months, from 1976 to 1978. The book is approximately 360 pages long (depending on edition), and appears to be a visual encyclopedia of an unknown world, written in one of its languages, a thus-far undeciphered alphabetic writing.
A copy of the physical book costs a small fortune, but luckily we have the interwebs at our disposal. My much-loved PDF copy of the book is available below.