Chapter 4: advance to German trenches
 

after finding key in castle I receive the task to advance to the German trenches. there is broken airplane and tank there and endless zombies. I can not find where to go. all territory is surrounded by wires

There is a pass that's hard to spot. Go back to the door where you came in, then "keep to the left" (you might see the zombies on the other side already). At some point, you will be able to go left (there was a wall-like thing - don't remember exactly what it was).

I think you need to kill most of the zombies, that will activate the script and open your way further (some of the debris will explode and allow you to continue)

But I`m not sure if we both talk about the same place..

Karel was right
 

Karel was right. Thanks