Codex Seraphinianus is a much-sought-after, very weird book, now available as a free (slightly dodgy) scanned (low-rez) download via the Internet Archive: "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."
As JWZ notes: "During my childhood, this book was treasured unobtainium. And now it's a click away. This post-informational-scarcity world is weird."