The Nexus/Find Elevator
At this stage, all you need to do is fighting. Developers decided to give you the chance to eliminate all enemies, which you have encountered in the game.
Walk straight ahead. Stroggos will close the door behind you and run into you from the other side. Few perfect shots from Grenade Launcher should do the trick. Walk trough the gate, which enemies fell into the hall 'with'. Turn left and use the panel (#211). Move forward.
After short walk, you'll find yourself in relatively big elevator (#212), protected temporarily by Light Tank and some Tacticals. Push the button to travel down. The Stroggos will rush into the lift through panes. Use Shotgun to eliminate them. When the elevator will stop, another fight awaits you. This time you'll face the Gladiator, Iron Maidens and Tacticals. Kill them and move forward.
Eventually you will get to the big hall. There's the teleport in the center (#213) and you can't destroy it. Quickly run ahead with only available patch and call for the elevator. Mind Tacticals during the ride. After the fight, move forward. After a while You'll reach the lift cage that will take you deep into the complex.
Scan Failed: Lock Down
After short ride, you'll reach the hall with TV screen (you can see Makron on it). Wait until the door will open and start the enemies' extermination. Than approach the place, where the screen was located in and jump onto the pipes (#214). Walk trough the tunnels to the ladder (#215) and climb up.
Gather ammunition and move forward. Use the elevator - you will get to the security's room. Push the button (#216) that unlocks all doors in the neighborhood and return to the lift cage, which brought you on this level. On the left side you'll find the gate. Walk through them to get to the next part of the complex.
You'll find yourself in the big hall (#217). Reload all weapons, save the game and move forward when you'll be ready for the really though challenge. Now, you have to face three groups of monsters: Light Tanks, Heavy Hover Tanks and Stream Protectors. The fight won't be easy, so use Dark Matter Gun, but also save ammunition for Makron. End battle with victory and move forward.
At the end of the route, you'll see the ladder. Climb down, get onto the pipes through the bay and run on the other side (#218) of the vast hall. Climb the next ladder up and jump over security barriers towards the pipes on the left side. Finally, you'll get to the last platform with the only available door.
In the next room (#219) turn right find the ladder leading down. If you use it, and then run the long tunnel, you'll find armor. Climb back up and encounter the last big group of monsters. Kill them all and walk through the door. Push the button (#220) to finish this level.