There are fast zombies on this level. They take three hits to kill. After this you'll see a circular panel on the wall. A gun turret comes out of it. Go up the ladder and across. Head down the ladder for a small red cross and another zombie. Make your way to the right to destroy another turret. Grab the . Take the ladder and grab the gun. Continue to the right. Take the ladder up and right. Cross the platforms and eventually you'll find a and, below it, a . Head up and left across the platforms. Eventually you'll find some ammo and a red keycard. Head back right and drop straight down, then head left, take the ladder down, and then the ladder after that. Down here you'll find a crystal, and, further to the left, a much-needed ammo and . Head back to the right and take the ladder you went past before. Grab the .
Take the first exit on your right if you want a big red cross, otherwise continue upwards. Grab the crystal and disable the forcefield, then continue taking paths heading right and upwards. When you reach the ladder with a hole in the ceiling, jump up and grab the armor and ammo, but don't go down the sides, instead head back inside and down the ladder to the right and then continue right.
You'll pass a big gun that you can use to shoot the parachuting zombies (press to enter/exit it, and push the direction away from the one you're facing to rotate it) but it's just as easy to keep going to the right to avoid them altogether. Climb the ladder for ammo and a crystal, then drop down for an . Jump across to the left-hand platform and head left. Take the upper platforms to get the grenade launcher, then drop down and head left. You'll find some more minigun ammo, and finally a yellow keycard.
Head back to the right and this time drop down the hole. Grab the big cross and open the forcefield. In here you'll fight some aliens. They attack by firing a gun that blasts them backwards. Go to the upper right and grab the blue keycard. Take the middle left platform for grenade launcher ammo. Now head to the right. Grab the small red crosses and head left across the gap for an . Drop down and head left for an . Head down and down the ladder and open the forcefield.