You've now arrived at the Genetic Engineering Biolab areas of the Citadel. This level has a very cool layout and design, and there are several interesting objectives to complete. Look behind you when you first enter the level. This passage looks as though it came from the last level in the factory area (and the message you get suggests it too) which makes it look like the boss level you just came from was some sort of diversion and off the main path. The boss encounter could have been an after-the-fact addition during the game's development. Anyway... There're missiles in the dark here, in case you need them.
First areas[edit]
Enter the tall room ahead. The far door will be locked. Jump down to the bio-muck below, where there are two grates and channels. There are a ton of Gryklaan around here. In narrow spaces it's easier to use first-person view when fighting them if you normally use third-person, because your character's sprite won't be in the way. If you want (you can skip this), go up the brighter-lit of the two channels. In the looping passage to your right, look along the outer wall for a darker section: behind is a secret area. (It's hard to make out--just bang on the wall as you walk by and you'll find it.) This section dead-ends, but there are items and stuff. Throughout this level and the biolab area overall, there tends to be a lot of items and ammo submerged in bio-muck tanks and channels. Be sure to look on your automap for the ammo/item symbols whenever you're around it. Another thing: if you see green bio-muck dripping from the ceiling, try not to let it drip on you, because it usually stings a bit.
When you're done, go down the darker channel across the main room. The grated-off channel to your right drops down a shaft and you'll be killed, so avoid it. Down here is another tall room filled with bio-muck. Go up to the ledge and control area, and to the wall with the caution texture. A door here opens; hit the switch inside to unlock the door back in the first room. Before going back, jump out to the platforms above the bio-muck. Next to one of those three green pipes there's a Secret Level Access Keycard floating in the air. Snag it, then go back up to the upper level in the first room, to the door you unlocked.
(A technical side note: this first room features what's probably the most elegant use of adaptive polygons in the game. These work by "flood-filling" sectors made of four lines, at a specified height and thickness, and are used throughout the game for upper floors, bridges, pipes, etc: anywhere you see large or irregular-shaped platforms and structures in between the main floor and ceiling. In this room five of them are used for the upper level; you can see them outlined on the automap.)
Go to the next room, where there are spawning tanks or something, and a central control booth. In the back behind the forcefield is the disinfecting chamber, which acts like an airlock of sorts to further areas of the level. Take the lift to the control booth and hit the switch to drop the forcefield. Whenever you go through the disinfecting chamber, hit the switch by the door first, even if the door is open. Then hit the switch inside to activate the chamber. (This is just one of the things that makes this level COOL.)
Two biogen pumps[edit]
Go through the chamber to the corridor beyond, where there are two paths. To the left is the biogen reservoir. There's nothing to do there yet until you've shut down other equipment, but you can clear out enemies and see what it looks like if you want. Take the other corridor instead. Before you get to the door, look for the different texture on the right: there's a secret area inside with lots of items. Go through the door to a very large room spanned by a bridge, with two biogen tanks and plumbing. (There's a Weapon Enhancement Chip submerged in one of the tanks.) The door down on one side goes to one of the biogen pump rooms, but is inaccessible while the pump is on. The "bridge door" at the far end of the room is locked; hit the switch down on the ledge to your left to unlock it. (That other switch on the ramp gives a message but doesn't seem to do anything else.)
In the next room there's a tall locked door which goes to the Biogen Pump 2 control room. Continue past this room and down the corridor (watch for Droppers that spawn in this area), which goes to a T-junction, the left side of which is blocked by triangular bars. Take the right corridor, which goes to the Biogen Pump 1 control room. Hit the switch to shut down the pump. This also opens the door to the Biogen Pump 2 control room; you can see it on the console to the right. Go back to that door, through another spawn-tank room, to the control room, and hit the switch to shut down the second pump.
Bio-neural regulator[edit]
Next, go back to the large room with the bridge, and through the side door to the pump room. On the other side is a small control room. Hit the switch inside to lower the triangular bars at the far end of the level.
Go now to the corridor with the triangular bars, and continue beyond. The bio-neural chamber at the far end will be blocked by a forcefield. Go first to the tall and deep chamber off to the right, jump from pillar to pillar to the ledge at the far side, and hit the switch to lower the forcefield. Then go to the bio-neural chamber and destroy the two power conduits to shut down the equipment. Now you can drain the reservoir and complete your tasks here.
Reservoir[edit]
Go back through the level to the biogen reservoir. Hit the switch: the level lowers, revealing a much larger area that was flooded before. Down in the bio-muck at the far end of the reservoir are two Death Spheres. You might want to use one to waste all the launchers and bad guys in here. When you're ready to leave, jump along the platforms above the reservoir to the overlook at the far end. The teleporter exits the level.