A waterfall known as The Devil's Kettle empties water into a hole and nobody knows where it ends up!
18
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 are pictures of Knights fighting Snails in old Medieval manuscripts - and nobody knows why.
23
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