The Voynich Manuscript is a mysterious book, recently confirmed to date to the early 15th century, that some people believe to be the real Necronomicon. Of course, since the Necronomicon is a fictional grimoire invented by H.P. Lovecraft for use in his horror stories, there is no “real Necronomicon”- but the connections are interesting.
Lovecraft describes the Necronomicon as a mysterious and unholy book, written by “the Mad Arab Abdul Alhazred.” The Necronomicon was at some point in the possession of the Elizabethan wizard John Dee, and at a copy is supposed to be held under lock and key by the (equally fictional) Arkham University.
The Voynich Manuscript has also been associated with John Dee, it is certainly mysterious, and it is held under lock and key by Yale University. The writer Colin Wilson, in his Lovecraft Mythos stories, explicitly identified Voynich with the Necronomicon.
So, what is Voynich? Nobody really knows, because no one can read it- the entire book is in an unreadable code that has defeated the efforts of the most skilled modern code-breakers. It doesn't appear to be gibberish, though- textual analysis supports the idea that the text is in some kind of language, although it doesn't fit the pattern of any known language.
That isn't all. The Voynich Manuscript is filled with detailed pictures of plants, but the pictures don't match any known plant species. It has a large fold-out map, but the map doesn't match any known place. It also has odd pictures of women swimming in some sort of tubing network, and star charts that seem to show a spiral galaxy.
The Voynich Manuscript may not be the real Necronomicon, but a lot of people would like to know what it actually says!