Portal/Chamber 15

First room


The first room introduces you to the double fling.

Place an orange portal on the extended panel above the entrance, and create a blue portal on the floor. When you fall through, notice you tend to land on the checkered part of the floor. This time, create a blue portal on the floor on the checkered part, and when you fall through, aim to fall through the blue portal a second time, which will then give enough momentum to pass through the force field.

Second room


The second room has a pellet that needs to cross two forcefields. You can place a portal on the burn mark, however you cannot place a portal above the receiver without the one on the burn mark disappearing. Since to place the portal above the receiver, the other portal would have to be in that small area, you must get the pellet into that area first. Thus, place portals on the burn mark and another part of the wall, as shown in the picture, so that it flies into the other side of the room. Then, run to the receiver, and shoot a portal in front of both the pellet and the red light above the receiver. You must be sure to do this before the pellet disappears, or else you will have to start the process over.

Third room


As with the first room, you have to perform a double fling; however, you can't start the fling within the same room because of the flooring. Instead, after placing one portal on the high extended platform, you need to head to a side room to the left which has a staircase where you can create a portal and jump. When you go through, quickly fire the second portal (same color as the one on the other floor) on the checkerboard and you will be thrown through the force field.

Next, you have to perform a double fling to cross the second force field. Perform similarly to the first room.

You are now in a room where a pellet is bouncing against an angled wall, and scorching the side wall. If you try to place portals on the angled platforms, you will realize that not only is momentum conserved, but the angle of entry as well. Instead, shoot a portal at the scorch mark on the flat wall, as well as the same location on the opposite wall so that the pellet hits the other angled platform and continues to the receiver. Then double-fling yourself back to the other side.

You now need to cross a conveyor belt that's moving backwards, and a misstep will drop you into the water. The easiest way is to put one portal that you will constantly use just outside this corridor, and shoot the other color against the walls. When you can advance onto the platform, do so, and shoot another portal further down the hall. When the platform brings you all the way back, simply go through the portal again and advance a little further each time until you can get all the way into the final room.

Fourth room
A pellet launcher is firing a pellet downward, and the receiver is blocked by a double door.

The doors are opened by the buttons in the side rooms. You need to get a portal in both rooms to press the two buttons fast enough. Then, shoot the wall opposite of the receiver (the extended panel) followed by the scorch mark on the ground to get the pellet into the receiver. This has to happen very quickly, so it may take a few tries. The lift for the chamberlock will lower, and you can proceed to Chamber 16.

Alternatively, you can try a high jump to the exit. With your back to the platform that takes you to the exit, place an orange portal at your feet. Go to either of the other two moving platforms in the room. Stand on one until it reaches the top and place a blue portal at its base while looking down. While jumping through the blue portal hold the forward button to land on the exit platform.

Advanced

 * Room 1 requires using terminal velocity to accelerate yourself before flinging.
 * Room 2 has an additional forcefield, requiring a 6-portal combination.
 * Room 3 requires you to start the fling from the checkerboard, continued from a wall of the side room, and finishing by placing the portal on the floor. You may still miss the jump, however.
 * Room 4 has only the ceiling in the siderooms usable. Also, you can't try jumping to the exit.

Portals
A 14 portal solution involves: The strategy is to shoot a portal high on the wall downrange. The portal you are in will collapse, and as you are falling into the acid, shoot another portal nearby and lower on the wall, through which you can escape to the new higher portal. This tactic requires 4 portals to progress down the corridor so that room 4 is within view. Shoot your 5th portal onto the floor in room 4 near one of the active lifts. Shoot the 6th portal low the corridor wall to escape the acid, just like before.
 * 2 portals in the fling at Room 1.
 * 2 portals to detach the camera from the wall in Room 2. Use the camera to deflect the pellet into the receiver.
 * 3 portals for the double fling in Room 3, part 1.
 * 6 portals to traverse the corridor after Room 3, ignoring the pellet and receiver.
 * 1 portal in room 4, next to the exit lift. Ignore the pellet and receiver.  Use the active lift, and jump down into the previous portal on the floor (the one your shot from the corridor) to propel yourself up onto the exit lift.

Awards at 23, 19 and 14 portals.

Steps
Awards at 75...

Time
Awards at 105 seconds...