Cool video! As for #3, I'd say the tunnel is probably accessible by a vent that's in the middle of cell area on the floor. It is the same color and doesn't make a sound when you knife it, but it is not sprayable so you can find it by where sprays get cut off. I haven't tested so I don't know how much damage it takes, but I'm guessing a lot based on playing a few rounds of it.
![]HeLL[ Clan](styles/quark/quark/hell_noshadow_by_amin.png)