Fans of surrealism, fantasy, and late '70s European illustration should find much to groove on in Luigi Serafini's Codex Seraphinianus, a 400-page imaginary encyclopedia of a world similar to ours populated by bizarre creatures. The above site features a little background on the mysterious work, and links to illustrations. Totally out of print, used copies cost boogaloo bucks. (Or do they?) At least the Amazon link suggests other strange books, even if there's not a Codex in stock.
Serafini has a site, but it's under construction. There is, however, a site devoted to the Codex. And apparently Serafini is just updating the original "mysterious" work, the Voynich Manuscript.