Minefields, I just love minefields (as a GM, not in real life)
In the same way as with booby traps I want my players to fear mines for every step they take. Not that I want my players to just blow up randomly on unmarked minefields, that is boring to me and my players.
Once in a while you can always do this, having someone step on a mine and putting the others into the trouble to carry their bleeding friend out of the unmarked minefield. This might result in paranoid players always looking for mines.
The germans often placed mines of obvious observations points, places where officers or NCOs would likely stop to survey the battlefield. This might be only a few mines but sometimes they are not detected until long after the area has been secured.
The marked minefield can act as a barrier, having the players to chose another, less deadly? route or the possibility to save some time at a risk if they are in a hurry. Hard decisions. The marked minefield might even be fake with no mines.
I am mostly looking to have my players aware of the dangers of mines, marked minefields are just one method. The effect will perhaps be more obvious if someone the characters observes steps on a mine close to them. This might be a friendly or enemy soldier, a civilian or even cattle. Sometimes soldiers herded goats or sheep in front of them through minefields. Hoping that the cattle would trigger any mines.
And don't forget AT-mines. The germans sometimes burried AT-mines beneath loosly packed dirt so that the first few vehicles wouldn't trigger the mine. To conseal mines under the surface of a road they somtimes used a dismounted wheelaxis to make tire tracks.