2. The Voynich Manuscript
Published in the early 15th century, this 240 page vellum book was handwritten and filled with intensely detailed scientific diagrams of plant life â€” in a script and of foliage that has never before been seen on the planet. 600 years later, and even through the attempts of hundreds of cryptographers â€” both professional and amateur alike â€” there has been no serious headway in deciphering it. The manuscript has only really been noticed since it was purchased by a collector in 1912, at which point it was already missing another 32 pages, and it appears the order of pages has been shuffled multiple times through history. There are around 20-30 letters, depending on how you count, which appear to match the statistical distribution of real languages, but match nothing in Europe. If it's a hoax, it's from that time period, and the most detailed and subtle one ever produced. It's an intriguing book, and you can look through the entire thing, free online.