A bomb left over from World War 2 was recently found in Poland but before it could be moved elsewhere, it exploded. Luckily it was in the water and no one was hurt.
https://www.usatoday.com/story/money/fo ... 653043001/
If that bomb had been there that long (since WW2, which was in the 1940's) then it makes you wonder what else is out there somewhere. Scary thought.