Most bunkers were in line of 5, and connected by ditches/trenches. So, they almost were never by themselves (unless in some isolated aerea), but in lines, and connected to a network of trenches. As the war in Ukraine shows, trenches are still useful.
There was also communication lines, (hard telephone lines), in ditches about 1m deep, in order to survive nuclear / emp attacks.
When I was a little kid, we'd play hide and seek in those bunkers, or we'd play 'castle take over' with self made wooden swords, romans vs illyrians as kids. (Or Albanians vs Turks). Which team conquered the most bunkers, would win.
They were fun as a kid, but we had to watch out for wild animals (or snakes), take refuge on those bunkers.
Now most of them are being scraped, to recoup the metal, so there are few left.