OK in the sea of gushing I say we look at the trailer again. I'm watching it now and babies, fetuses and the like seem to play a big roll. There is even a baby doll in the very beginning. Yet all these things seem either very valuable or rare or at least something to be protected as we can see Del Toro's character clutching the uhh... bottle baby close to his breast and constantly looking about in distress at the death filled war torn landscape full of tanks and troops and... viscera. I'm guessing children and youth, typical symbols of life and purity are not something easily found in the game world, perhaps even strikingly rare and under severe threat. In the past trailer with Reedus he was also holding a child and there was a lot of umbilical cord stuff going on.
In general it seems to be a huge contrast between the living, the young and human and everything else. I'm going to make a reaching guess based only on a hunch that this is some kind of limbo or place where death is quite literally real. We see the tank driving by on the bridge above and its quite literally covered in guts and gore. Of course this could be an actual regular, and use the term loosely, earth where some soldiers have gone nuts and covered their tank with guts of enemies or innocents but with everything else as crazy as it seems I don't think its the real world.
Perhaps in this death and war filled nightmare realm is filled with spirits of the dead? Of course we have nowhere near enough info but even at the end when Del Toro's characters seems to take refuge inside the tunnel under the bridge and once again baby doll seen glowing and floating away leading us further inwards. Then we get the troops with Mads Mikkleson and tentacles or something under the surface of the sewer water. I'm honestly not sure what to make of this scene yet. Still digesting things but just make tank on things after a few viewings of the trailer.