#24 Underwater Ruins
Robert Marx, in 1982, found a field underwater with strange foreign remains in Guanabara Bay, Brazil. This field was as large as three full-sized tennis courts and contained over 200 ceramic jars.
These jars were discovered to be made of materials from the Roman era and were reportedly used by the Romans for trade. The mystery here was that the Europeans never came to Brazil until the 1500s!
Thus, it was never understood how these jars came to be found at Guanabara Bay.