Several hundreds of thousands of unexploded bombs still plague Europe especially in those German cities targeted by the very successful Anglo-American strategic bombing campaign.
(Before anyone emails me about Dresden, allow me to mention the following: Dresden was the center of the German optical industry and optics were a critical component in the war. The city had 141 factories manufacturing military goods for the Wehrmacht according to the records of the German Army Quartermaster General captured after the war. Military equipment was even being assembled in the fabled porcelain factories.)
I have written a lot about unexploded ordnance in Europe from World War Two so it is interesting to note that lots of bombs, artillery shells, and mortar rounds being used in the present day don’t explode, either, and create havoc. In this case, Libya is now littered with unexploded ordnance detailed in the following story from Der Spiegel:
I encourage you to read the rest.