When I was a kid living in Belgium in the seventies, we used to go visit battlefields.
I remember parts of the forests by Verdun were closed off because of unexploded ordinance from WW1.
The farmers were still finding things when they were plowing.
We went to have a picnic in a field, and in a little copse my brother found a rusty round thing. It was an unexploded grenade that the farmer must have put aside.
We also found a rusty and rotted rifle with bullet still in chamber.
I have that, still.