Key Item: Lv 7 key card
Boss Fight: Vulcan Raven
The area is set up in a grid pattern with boxes providing cover for you and Vulcan Raven. Start off by using your Nikita missiles to attack him. If you fly into his line of sight, he'll just shoot down the missile with his mini-gun. Try to fly the missile into his back. After two hits, Vulcan Raven will begin running, and your missiles have no hope of catching him from behind. Switch to your claymores or C4 and set traps for Vulcan Raven. If you've ever played a Bomberman game, you already know how to win. Drop your mines and C4 blocks in intersections, attempting to anticipate where Vulcan Raven will run. It won't take many mines before Vulcan Raven succumbs, and he gives you the Lv 7 key card. Walk north through the large doors.
Equip your thermal goggles. Notice the trap doors on either side of the ration in the middle of the hallway. Don't get suckered by it. Walk along the sides of the hall to avoid them. Around the corner, there's a guard patrolling the bridge, and one way up high looking out over the bridge. As the lower guard faces the other way, move out from the corner. The top guard will see you, and run down to investigate. Quickly whip out your M9 and shoot the lower guard in the head as he stands on the bridge. The guard from the top will stop and look at his drowsy comrade, which gives you a great opportunity to shoot him with the tranquilizer gun. With both guards asleep, you now only have to dodge the cameras along the far wall. Run up the stairs on the right to where the guard was standing watch, and grab the Stinger ammo, which you'll need soon. Run back down and into the level 7 door by the cameras.
It's Metal Gear! Make your way to the right and up the narrow stairs. Watch out for the guards patrolling the upper levels. Take out both of them and you're free to make as much noise as you like. When you're on the third level, loop around to the left and finally up to the control room at the south end of the room to start another cutscene.
Snake, you clumsy fool! You've dropped the PAL card. Run down to the bottom level, and go to the northwest corner. Notice the rat running around near the hole here? Shoot the rat and he coughs up the PAL card. Grab it and go back up to the control room. Toss a chaff grenade in there to spoof the cameras, equip the PAL card, and go to the laptop on the left with the yellow screen. Press the action button to insert the card.
Now you've got to freeze the PAL card. Backtrack to the warehouse where you fought Vulcan Raven. It's being patrolled by several guards that you can take out however you with. Equip your PAL card and stand around in the room for a minute or two until the card turns blue and has a "W" on it. Make your way back up to the control room and insert the card into the middle laptop.
Time for the heated version. Backtrack all the way back to the steam room in the Blast Furnace area. This means a long trip up both cargo elevators. Stand around in that steam room until your PAL card turns red and has a "Z" on it. Run back to the control room and insert the card into the last laptop. You've been had! The control room shuts and fills with gas. Equip your gas mask until Otacon rescues you. Leave the room and eventually you'll take on Metal Gear.