Your gonna start off in the airlock you left the last stage in, it will open up, and you'll end up on the Martian surface.

Two Cacodemons will spawn, pump them full of lead. Head forward to the next metal platform, walk to the opposite side of it, and up the ladder, walk down the path, take a left to collect some oxygen, turn around and kill the Vulgars and Cacodemons scattered about, keep moving, until you come to the airlock. Cycle it, and breathe fresh air.

Ahead of you will be a marine repairing a sentry bot. Talk to him, and take a right, to a door with a sign above it that reads "Maintenance."

This is a small room, with a door to your left, 2 Vulgars will spawn, kill them, and to the next room.

This is a corridor, a Vulgar will spawn at the end, followed by multiple zombies, when they are dead, go to the next area ahead of you.

A fat zombie will attack you from your right, shortly followed by a Vulgar, head down the stairs, ignore the door ahead of you, and down another set of stairs behind you. Another door will be at the foot of this.

Head down the small stair-set and collect the PDA next to a marine's corpse. Once you collect it, a zombie attacks ahead of you, and a Vulgar from behind. Turn around and go up to the access panel that reads "Armory". Go inside, and there will be two lockers, enter the code ’134’ and Tada! Collect the items, then head back to the sewage stairwell. Go through the door you ignored before.

Head down to the access panel at your left that reads "access tunnel". A Revenant spawns in front of it, and a Vulgar from behind. Kill them, and click on the access panel, and head through the door.

A sentry bot will be in front of you. This is the part where you ignore my babbling, and follow that little guy! Remember that he's not invincible, you watch his back, and he'll watch yours. You and the bot will encounter various numbers of Trites, zombies, Vulgars, and Revenants along the way. Just keep going down through the tunnels until you come to the double doors at the end.

In front of you, will be some broken-down double doors ahead of you. Head to the right, and up the ladder. Crouch through the small gaps until you come to a large, nasty looking room.

Hell Hunter: Berserk Strategy By - Fluffy Kitty

HELL HUNTER 2: "BESERKER"
Health: 1100
Attacks: Slash- 20; Bite- 25; Jump Attack- 70; Fireball- 20
Ability gained: Berserk

This guy should be even easier then the one before. First off, the only way you can hurt him is by shooting that red orb on his chest. I suggest the Double Barreled Shotgun (Actually, I absolutely insist). Simply slow down time with the artifact, and easily dodge his now slow attacks, then shoot the orb. When you need more souls for the Artifact, just use on of the many Marines’ bodies strewn about. While this fight is easy, the next one is... Tougher....

Once you have killed him, head over to the tram and exit to Phobos Labs: Sector 1.