Follow the corridor round and kill the imp that spawns in to your left and another behind you. Enter through the window to grab pick ups and use the medical station.
Use the control panel to open a cabinet and code 571 to open another then head through the door. Kill the wraith and three cherubs and then head right through the door and across the stepping stones.
Go through the door and take the first door on your left, kill the imp and the commandos, grab the pick ups at the back of the room and on the rack on your left.
You can check the screen in here to see the Lab A Meeting Room and get the code you need. Go back across the bridge and kill the trites in the Main Entrance Hall.
Enter the door on the left, kill the imp and grab the pick ups, come out and enter the next door for more pick ups then come out and kill the archvile. Enter code 627 to open the door.
Lab A Entrance
Follow the corridor round to the right and watch out for the floor collapsing. Jump across the floating bits and take the next door on your left.
Grab the armor behind the box in front of you and go right, kill the cherubs, the imps and the wraiths that pop out all around you. Use the medical station on your right and grab Charlie Haskell’s PDA from the desk on your left.
Go through the door and jump across the floating rocks to grab armor and a rocket launcher. Go back to the previous room and kill an imp and a commando, follow the corridor back round to the right and kill some cherubs then get into the lift on your left and select level 2, CPU Banks.
Lab A Upper Floors
A wraith will spawn in to your left, then an archvile round to the right and some cherubs behind you.
Turn left at the end and kill another wraith, then head right and grab the medkit on the desk. Turn round and find armor in an alcove on your right then some trites will attack. Get into the lift and choose level 3, Routing. There’s an imp to your left and cherubs to the right.
Go round to your right and kill a commando and then an imp to your left. Grab the ammo from the office on the left and go through the next door. As you walk in alcoves will open either side of you to reveal two imps and then a commando runs in. Grab the pick ups in the room off to your right and kill the two imps that spawn in, then kill a cherub and head up the corridor.
Take the door at the end on the right, kill another imp and grab the items from the open cabinet. Use code 468 to open the other cabinet, kill the trites and imps then an archvile and some cherubs.
Lab A Upper Floor Offices
Retracing your steps back through the offices, kill a couple of cherubs and then make your way back to the lift and take it back down to level 2. As you follow the corridor three wraiths will spawn in front of you and one behind.
Take the lift back down to level 1. Go left through the door, over the floating bridge, through the next door and as you come round to the right an imp will spawn in on your left. Continue through the Elevator Access Hall where two imps will spawn.
Turn left and get into the lift and choose 1 – Main CPU. Follow the corridor round to the right and watch the marine die. Before you enter the bay door on your left drop into the hole in the floor and crawl to the next room for some pick ups.
Go back and enter the bay door to exit the level.