Funny that I thought Blackhawk Down as I read through this.
The movie really shows how tough it is to make head way against determined opposition.
There is a very under-rated movie titled Stalingrad that anyone contemplating the rigors of urban combat in a blasted ruined city should see. Do yourself a favor.
I ran Armies of the Night four times. Not one party even got close to the gold. Just traveling a one kilometer could take days of scouting the route, dodging enemies, getting ambushed,
doing first aid, finding clean water, losing and finding gear, getting lost, going underground, going rooftop to rooftop, rafting through the subway **shudders**,
helping innocents, etc. Mix and match for best effect, like getting ambushed while being lost, it really puts the PC's in a pickle.
I highlighted first aid and helping innocents because those are huge time killers that could turn a two hour walk into a 2-3 day nightmare. It does not just have to be innocents as well, it could be an injured officer, that offers the party a semi-current map of the area if they help get him somewhere safe.