Wait It Gets Worse!
When the elevator stops, go through the opening, left and then straight. Your blue floating friend takes off on you, and of course the enemies come. Let the yellow friends help you out with them. You'll find health in one of the ditches. When the right's over, head to the right.
More enemies. Yet another 'wait here' at a door. More enemies. The door opens, go right and right again. Down into a trench, and this one has a tunnel in it. Go through the tunnel, and at the other side there are lots fo enemies. Grenades work well in these tunnels :)
Blue-fiend now says, "Your environmental suit will protect you well when flood begins to alter the atmosphere. You are a good planner." Oh lovely. This is the cue for the enemies to launch a massive attack on you, so be prepared. If you've been killing everything as you go, you should have plenty of ammo. I love the shotgun for the bigger monsters.
Now go through some pillars, past some blue screens, then right and right again. There's a few guys up on boxes to kill.
"This facility was designed to research the flood. I am glad some of them survived to reproduce." Some of them?? More fighting. You reach a door, and he says he'll deactivate it - wait here. He laughs maniacally as he leaves you because of course tons of monsters attack. Grenade them. When the door opens, the yellow floaty guys are there to help.
"Please stay close" he goes. Sure, if he would just let you follow him! You hit another circular lift to go up.
Halo 2 Walkthrough
Halo 3 Walkthrough