There is a mysterious and loud radio signal known as 'the space roar' that has yet to be explained.
15
There are pictures of Knights fighting Snails in old Medieval manuscripts - and nobody knows why.
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There is a 600 year old 240 paged book called the Voynich Manuscript, that’s written language is still completely unknown today.
15
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
A waterfall known as The Devil's Kettle empties water into a hole and nobody knows where it ends up!
18