As a German living in Berlin it's still pretty normal that once in a while WW2 bombs are found during construction. Heavy bombs that didn't explode probably penetrated the ground quite a bit so when rebuilding it was probably just easier to just leave them there. That's just a guess.
There are also still bombs and grenades in the rivers. There are some magnet fishing YouTube channels where you can occasionally see them pulling up stuff like that.
There are also still bombs and grenades in the rivers. There are some magnet fishing YouTube channels where you can occasionally see them pulling up stuff like that.