Roanoke Island
The lost colony is Roanoke Island is one of the most popular historical mysteries of all-time. A group of British settlers made Roanoke Island home but were left struggling to survive. John Smith left to go get supplies and returned a few years later to a completely empty colony. The only clue was the word "Croatoan" carved onto a tree. The settlers were never found.
Richat Structure
The Richat Structure is also known as the Eye of the Sahara. It's a 30-mile-wide bulls-eye-looking feature that can be seen from NASA's space stations! Researchers initially thought that it was a meteor impact site but now believe it's just from erosion.