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
Since 1982, a radio frequency emanating from Russia has been broadcasting a buzzer-like sound and, periodically, an unknown voice reads orders, names, and numbers. No one knows where exactly it is coming from or what it means.
13
A waterfall known as The Devil's Kettle empties water into a hole and nobody knows where it ends up!
18
There is a mysterious and loud radio signal known as 'the space roar' that has yet to be explained.
15
Scientists lit a cave of natural gas on fire in 1971 expecting it to only burn for a few days; it still burns to this day. It has been nicknamed "The Door to Hell".
19
There is a 600 year old 240 paged book called the Voynich Manuscript, that’s written language is still completely unknown today.
15