Photos of truly massive piles of spent artillery shell casings helped this click for me [2]. Even if the artillery detonates 99% of the time, we're still talking about hundreds of thousands or maybe millions of unexploded shells.
People will be stumbling into unexploded butterfly mines and cluster munitions in Ukraine for generations.
[1] https://www.youtube.com/watch?v=YNIBE64CAgs
[2] https://64.media.tumblr.com/37a01168a1c386fa1657ae35ce0d0508...
https://en.wikipedia.org/wiki/Iron_harvest
Choice quote "The French Département du Déminage (Department of Mine Clearance) recovers about 900 tons of unexploded munitions every year."
Seeing small stacks of rusted ordnance neatly at the entrances of fields is a common sight. Farmers dig them up each year, and put them aside. Bomb disposal does regular rounds.
You'd drive through the region, and the most noticeable remnant of the Great War are the graveyards. However, the War itself is still very much there, just a few odd centimeters buried in the clay soil.
[1] https://www.france24.com/en/20140319-wwi-shell-kills-two-nea...
Just wanted to add to the point that the history is all around us, it's not neatly cordoned off and put in museums.
If you travel on the Eurostar train from Paris to London...... before boarding at Gare du Nord station you will pass a French bloke by the escalators employed to hold a placard with a sign in English saying not to take unexploded ordnance on the train.
This is because a few years back, some fuckwit did just that, shutting down the channel tunnel for several hours.