The City of Munich is no stranger to bombing.  Many of it's citizens were evacuated to deal with an American 550 lb bomb.  In the video below, the bomb is shown being detonated.  Reasons given were the fuse was a chemical type which the bomb guys weren't eager to tackle.  Some WW2 bombs had anti-tampering fuses which were intended to slow down or possibly defeat the men who dealt with unexploded bombs, creating more havoc after a bombing raid and further demoralizing the populace.  Or maybe they were thinking about the 1000 lb bomb the Germans tried to defuse in Goettingen in 2010 that exploded, killing the bomb disposal crew. 

Bomb in German churchyard

  The grim reality is many people every day walk over, around or close to bombs or otherwise explosive ordnance that has been buried and forgotton.  This is true for wherever you live, as long as there was a war there in the last 200 years.  Those wars won't be over till the last bomb goes off