Once you're back on the right floor, go right and across the gap in the floor. Follow the given path until you reach a bright passage below. On your right, there is a plank that you can use to jump over to the other wall. Do it, then jump down next to the passage.
After stepping into the new corridor, a nice psychopath will welcome you - he won't have any evil intentions towards you, though, but will only close the gate behind you so that you can't go back. There's no other way, so proceed on.
Squeeze through the shelves until you see the large guy breaking into the room at the end. Leave him be and go into the room on the left. Look up to see a shaft entrance. Get to the other side.
Use the corpse-barricaded exit. You need to push it to go through, but when you do, you'll find yourself next to the library that you passed by at the beginning of the game. You can find a battery here and some documents describing the plot.
Use the same door to leave, then go right. In a moment, you'll be back in the reception area, and the talking nut will tell you about a key that you need to find.
Make for the open door and go down the corridors. Eventually, you'll have a door on the left and a dark room. Use the slightly damaged video camera to find another gap inside. Drop down, then use climb up the ladder.
Approach the wall and walk along the ledge to the other side of the location. That way you'll go around the metal gates and the locked passageway.
Jump down and go ahead, and when you step into the brightly lit room, use the door on the right. You're going to need to jump again to find yourself in the cinema room.
After taking a few steps, the movie will start. You can either watch or not. Either way, go to the back and you'll see a door behind the chairs. Go through it, then through another one. Walk past the lunatic hiding in a locker and go up the stairs. If you go straight on, you'll find a document.
Upstairs, crouch and go under the desk; you'll see the door to another room with batteries inside. Take them, then attempt to open the next door. You won't be able to, so backtrack to where you needed to crouch.
Wait until the lunatic goes downstairs and step into the balcony. On the left you'll find a way to the other side. At the end, jump over to the next balcony, enter the room and take the key you find there.
Now you need to go back to the reception area. As you go down the stairs, you'll listen someone banging on the cinema room door. Wait until that someone goes inside, then escape through the passageway he made open.
If he doesn't notice you as go by, you'll have peace and quiet. Go back to the reception area and open the gate leading further up.
Upstairs, use the regular door on the right. Through the double door next, walk into a large hall with a lot of chairs and tables.
There should be another passage on the left. Go down the corridor until you reach a gap in the wall at the end. Go through it.
You'll find yourself in a room with two poor souls praying. Run into the corridor. In the middle room on the left there is a window passage. In room B329 you can find some documents, and at the end of the corridor, a battery.
Use the ledge to get into the open room, and leave it. Make your way to the right, then right again, past the two guards at the double doors. Go to the middle of the church and take the other key.
Listen to what the crucified Martin has to say, then leave the room the same way you came in. Turn right.
You'll find a ventilation shaft. Use it to get the hell out of this damned place. Jump down and go down the corridor - that's when your favorite person shows up. Run forward, taking some hits and squeezing past. At the end of the corridor, enter the room on the left and jump up through the grate to find yourself in the kitchen.
Leave the kitchen through the door on the right and you'll find yourself back in the hall. Use the elevator.