There is a mysterious and loud radio signal known as 'the space roar' that has yet to be explained.
15
There is an island near Italy that was the site of wars, a dumping ground for plague victims, and an insane asylum. It's considered so dangerously haunted that the Italian government does not allow public access.
78
The exact cause of death and burial site of Genghis Khan is unknown, because all of the 2000 funeral guests and 800 soldiers were killed in order to preserve the secret.
16
There is a 600 year old 240 paged book called the Voynich Manuscript, that’s written language is still completely unknown today.
15