The Platypus used to be considered a myth like Bigfoot and the Yeti.
18
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
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
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