Abandoned

A walkthrough map included in Sven Co-op 4.0 to 4.07.
Note: Some of the screenshots are outdated.

The story as written in the MOTD:
You and your colleagues knew that the resonance cascade would happen. It was inevitable. The administrator was more concerned about profit than the fate of the human race.
But it's not too late to save earth. You and some of your colleagues ventured deep into the abandoned parts of Black Mesa to find the unfinished plans for the GTIS, or Global Transdimensional Intrusion Shield.
With the plans for this, we could stop the aliens from ever coming to our planet. Or should the horror happen before mankind is fully prepared, at least stop more from coming.
Unfortunately, hell decided to break loose just as you found the documents. Screams are heard from outside the old archiving room. Barney and Fred were supposed to keep guard, but now they're being zombified. Shit happens.
You need to escape NOW, and you need to get the documents with you. Fortunately, being the gun-nut Barney is, he left some extra weaponry at our SUVs. If we can get to the SUVs, we can ride through the tunnel system, up the main entry lift, fight our way to the lambda guys, and save the world. Let's do it.