The Two Colonels: Right after you clear the first hallway of slime, the diary will be lying on a desk right in front of you after you go through the door at the end of the hallway.
I gotta admit it, that Andrei does have a good head on his shoulders... These tunnels were always easy to get lost in, but when they get covered in slime, even a map can't help - it's enough for it to cover some passages to change the shape of the place completely. The road signs truly are a godsend here, they're highly visible and the slime can't eat them.
We only had to ask our guys to grab some signs when they return from the work at the old railroad, and they brought a whole bunch in no time. Now we can't get lost here even if we wanted, and the OSKOM guys will have an easier time finding their directions, too, once they finally decide to visit this place with their flamethrowers. Why didn't I think of this earlier? I really should arrange a bonus for him, he's earned it fair and square.