15. Voynich Manuscript
The Voynich manuscript is one of the most talked about books of the 20th century. It was discovered by an antique bookseller in 1912 and is written in an unknown alphabet with depictions of nude women and other strange symbols. Scholars have dated the manuscript at over 600 years old. While some believe it is an elaborate hoax, others believe it is the discovery of a new alphabet. Unfortunately, no one has been able to decipher it.