In this level, you have to escape from the Apartment Block getting out the back door of it, eventually reaching the top (fourth) floor. This is a somewhat timed event, because the gendarmes break down the door to the apartment building and throw gas bombs inside. If you do not make it to the top soon enough, you will die from the gas. Additionally, if you run back down the stairs and approach the entrance where the two gendarmes are waiting outside, Lara surrenders and the game is over.

There is a movable metal locker on the left. You can pull it in front of the doors, but this will not prevent the gendarmes from breaking into the Apartment Block. If you do not pull the metal locker, they enter the building when you step on the second set of stairs. If you pull it, they enter when you turn right on the first floor. If you want, you can then go back down again and kill the only gendarme that enters the building, or wait until later and take the advantage of the elevator that can take you up quickly. Since you have no ammo in your possession, you have to kill him hand-to-hand (thanks to SYS for letting us know about this kill).

The door on the left will not open and the elevator is out of order (for now). To proceed, you have to use the stairs.

1st floor - Go up the stairs to reach the 1st floor. At this point, the gendarmes break in. There is nothing to collect or do here. Get to the second floor by jumping across the broken stairs.

(Note - If you are having troubles with the gas bombs that the gendarmes throw, you can avoid triggering their appearance and reach the top floor at your ease. When you go up the first flight of stairs, turn around to face the opening in the stairs that connect the 1st and 2nd floors. Take a running jump to grab the edge of the opening and pull up, as shown in this screenshot. Turn around, jump the gap and continue upwards. The gendarmes appear when you reach the 1st floor and since there is nothing interesting there, you can completely avoid it. Thanks to Shrensh about the hint.)

2nd floor - As soon as you reach the second floor, some rocks of the derelict apartment fall down, collapsing the floor on the right. There is a locked door on the left and you need a key for that. Take a running jump over the gap, grab the opposite side and pull up. Follow the corridor to a short hallway and pick up the Health Pills (20% of health). Exit the hallway and pull the movable armoire away from the stairs. Go up to the third floor.

3rd floor - Pick up the Small Medipack (60% of health) in the hallway on the left and open the door to get a strength upgrade. Look inside the two green cabinets. Get the V-Packer Cartridges from the left and the K2 Impactor Battery from the right one. Exit, follow the hallway to the opposite side and pick up the Health Bandages.

4th floor - There is a movable box at the top of the stairs. Pull it, go behind it and push it to the edge of the stairs. You cannot move the box if you have not got the strength upgrade. Climb on the box and turn to face the railing. Take a standing jump to grab the railing and pull up. Open the door on your right and pick up the Lift Maintenance Key from the floor. If you want, you can end the level by opening the door on the left, using the Maintenance Key. If you want all the pick-ups, get the Apartment Key from the hook on the wall and use it to the locked door of the second floor.

Back to the 2nd floor - Use the switch to call the elevator. Exit the room, enter the elevator and press '2' to go to the second floor. Exit the elevator and jump across the gap. Go straight to the hallway and use the Apartment Key to open the door. Get the Vector-R35 Gun from the locker, the Chocolate Bar from the left drawer of the desk and the V-Packer Cartridges from the right hand drawer. If you want, you can go down and kill the gendarme that has entered the building. You have to be quick though, because if he draws his weapon, Lara will surender. Make your way back to the sevond floor, enter the elevator and go back to the fourth floor. Enter the room where you used the switch for the elevator and open the door opposite the entrance.