Room #13
This is a rather tricky room. Open a portal next to the cube and button. Place the cube on the button. Enter the open door. Activate the platform with an energy ball (you've probably learned how to do this by now). Open a portal above the electric rails and in a convenient location.
Wait for the platform to arrive and jump onto it. Take the cube. Send it to one of the buttons. Return to the starting position. Send the first cube (the one you used to open the door) into the hall. Place it on another button. The door will open. Move through it.
Room #14
Immediately after entering the room, turn left and go forward. As soon as you start approaching the raised area, steps will extend in front of you, allowing you to climb up. However, after doing so, they will immediately retract. Pass the energy ball receptacle and turn left; you'll see a cube on the raised area.
Now turn around and place a portal on the wall behind you (opposite the raised platform with the cube) as high as possible. Now go to where the steps were; there's now a small drop. Place a second portal at the bottom and jump into it. You should fly out of the first portal fast enough to reach the raised platform with the cube.
Take it down from there, but before you leave, place another portal above the energy blast receiver.
Next, drag the box to the beginning of the level. There's a button there. Place the cube on it, which will open the door at the end of the corridor. Enter it, and you'll find yourself in front of a small water barrier. Jump forward along the moving platforms. Behind the barrier, you'll find a small room where a cannon fires energy bolts.
Place a second portal (you placed the first one above the receiver after you pulled the cube from the elevated area at the beginning of the level) on the wall so that the ball fired from the cannon hits it. After this, the ball will fly out of the first portal and land in the receiver. This will activate the elevator near the beginning of the level, which will take you to the exit.
Room #15
Is a large room. Exit the elevator and proceed forward. Fly over the fence with a double throw. In the second part, there will be two sections separated from the main corridor by force fields. There's another fact, or rather two facts, worth considering here. First, you can't shoot portals through these force fields. Second, when you pass through a force field, all the portals you've placed disappear. Therefore, you can't place a portal on one side of the field, pass through it, and place a second one on the other side.
The section closest to you contains an energy receiver, and the one farthest away contains a cannon that fires projectiles. Place the first portal so that the ball, after leaving the cannon, lands directly into the portal. Place the second portal opposite the section closest to the exit, containing the receiver. Now you need to move a little. Enter the section containing the receiver and wait for a ball of energy to fly out of the second portal toward your section. As soon as this happens, place one portal in the section containing the receiver so that the ball of energy flies into it, and the second portal directly above the receiver so that the ball exits and lands in the receiver.
The platform will lower, and you'll use it to ascend further. You'll find yourself in a huge section, with a glass wall in front of you and a force field above it. Therefore, using portals won't work. So, turn around and place a portal as high as possible on the wall behind you. Then, turn left and climb a short flight of stairs. There's a small ledge there; place the portal at the bottom of the ledge.
Now, get ready for some action. Jump into the portal at the bottom of the ledge, after which you'll fly out of the first portal at the top of the wall. While you're in flight, you need to fire the cannon below you, where you'll fall. This will cause you to fly into this portal and then back out of the portal at the top of the wall. Just use the speed you've accumulated during your fall. This time, you'll be able to fly over the glass wall and through the force field.
You'll find yourself back in a large room with a glass wall and a force field over it. Again, place a portal on the higher wall, and a second one on the floor. Jump into the second portal and cross this glass wall the same way as the previous one. On the other side of the force field, there will be two slightly recessed walls on the wall. Place one portal to the left and one to the right, opposite these walls.
After some simple teleports and clever wall slams, the energy ball fired from the cannon will hit the receiver. Jump back over the force field the same way you got here. The platforms will begin to move, but they'll be moving in the opposite direction, so you'll need to use the portals to cross them faster than they move.
Room #16
Here you'll encounter combat turrets. They can rotate to lock on to a target; their current direction is visible by their red laser sights. Disarming them isn't difficult; simply knock them to the ground, any way you can. You'll recognize some of them as you progress through this level.
The first turret you see will have its back to you. Back up a bit and place a portal on the wall, then shoot the second portal directly under the turret. It will fall through it and fall out of the first portal onto the ground, flipping over. It's useless from here on.
Continue on and you'll encounter a second turret, aimed in your direction. Carefully peek around the corner and place a portal under this turret; it will follow the first. The third turret will be on a hill, so you won't be able to place a portal under it.
However, there's a cross on the ceiling above it. Place a portal there. Afterward, return and grab one of the "overturned" turrets. Then, return, place a second portal somewhere nearby, and throw your cargo through it, right onto the working turret.
Walk forward a bit and you'll come across two boxes; they'll come in handy. The next turrets are destroyed in the same way as the previous one. Place a portal above the turret, then a second one next to it, and throw a box into it. Soon you'll find yourself in front of a closed door.
There's a button next to the door; place the button on it and the door will open. Beyond it, two more turrets await. You need to deal with them a little differently: place a teleporter behind them, and the second portal directly in front of you. This will put you behind them. Simply knock them over to disable them.
Room 17
Here, you'll need to use a box with a heart. Nothing special, just a simple box; you'll just have to drag it across the room. Your first obstacle will be high curbs. Simply place a box in front of them, jump onto the curb from it, then turn around, crouch, and take the box with you. You'll reach a narrow passage with a ball of energy floating along it. At the end of this tunnel, opposite the cannon firing charges, place a portal.
Then grab the crate and proceed through the tunnel, using the crate as cover. There'll be a second tunnel beyond this one. To proceed through it, wait for the cannon to fire a charge and then follow it (using the crate as cover). Be sure to let the charge go first, otherwise you'll get hit in the back.
After passing through the second tunnel, jump off the platform. There will be three lowered platforms on the right. Go into the left room, where the cannon fires energy charges. In the same room, there's a receiver on the wall. Deflect the charge so it flies into the receiver. This will raise the first platform.
After this, exit the room and head left, passing two closed doors. There's a button on the raised platform to the left. Place your cube friend on it, and it will open one door. Now return to the first door and place a second portal directly across from the doors. Step on the second button to open the second door. Wait for a bolt of energy to fly out of your portal.
It should fly past the two open doors and hit the receiver. This will raise the second platform. The third is even easier. Place your box on it and face the remaining two platforms. To the right of them, you'll see a slanted plate. Place the portal on it and wait for a bolt of energy to fly out. Afterwards, the bolt will hit the ceiling and hit the receiver.
This will activate the third platform you're standing on. Once you've reached the top, jump off the platform into the tunnel and follow it until you reach the button. Here, you'll have to part ways with your friend. Place the cube on the button and go through the opened door, press the button there, and then return to the cube. Pressing the button will temporarily open the furnace. You need to grab your friend and throw him into the furnace. This will open the door to the next room.
Room #18
Is a fairly simple, but long room. From the very beginning, shoot a portal at the ceiling above the opposite side of the cliff. Place a second portal next to you and step into it, this way you'll cross the first gap. To climb the next ledges, do the same. Shoot the ceiling above the ledge, place a second portal next to you, and step into it.
Soon you'll reach a button that opens the entrance to a room full of turrets. There, a cannon periodically fires energy bolts. As soon as you enter this room, the plate that opened the entrance for you will retract. To deal with the turrets, simply place a portal where the energy bolt hits, and place a second portal opposite the turret. To position the portal more accurately, use the sight beams as a guide.
After all the cannons are destroyed, look to the left side of the platform. There, on a narrow ledge, you'll see a pole with a button. Next to this ledge, you'll see a small hatch covering a receiver. Here's what you need to do: place a portal opposite the hatch, on the opposite wall. Wait for the energy ball to fly through your first portal again.
As soon as this happens, make sure the ball has exited the second portal and is heading toward the hatch. Quickly place one portal next to you, and a second one there, but slightly higher. Enter the portal and jump out of the second portal. Press the button on the ledge to open the hatch before the energy ball reaches it.
As soon as the ball hits the receiver, the moving platform will come to life. Stand on it and roll to the very end, then jump down to the ledge below. There you'll find a button on an iron pole. Shoot one portal back to where you came from, place the second one next to the button, then press it.
Then quickly jump into the portal; this will take you back to where you came from. After you press the button, a slab will extend and become tilted. Place the portal on it, then move left. There, at the bottom of the cliff, there won't be water, but a platform.
Place the portal on it and immediately jump into it. You'll fly into it and emerge from the portal on the tilted slab. This will allow you to reach the ledge with the cube. Grab it and use the moving platform to cross back to the crate. The retracted platform will allow you to escape this room. Exit and go to the large button, place the crate on it, and exit through the door that opens.
You only have one last effort left. Now the procedure is as follows. Place a portal on the platform above the water. Turn left and place a portal at the bottom of the chasm, then jump into it. You'll fly into this portal and fly out of the first one on the platform vertically upward. At the apex of your flight, you'll see another platform.
Place a portal on it and fall down. You'll fly back into the portal you placed at the beginning and fly out of the portal on the higher platform vertically upward. At the apex of your flight, you'll see another platform. Place another portal on it and fall down again...and so on until you reach the exit.
Room #19
At the very beginning, you'll see two tiles arranged in a pyramid. Above them will be a cannon that shoots energy clots and a receiver. Place the first portal on one tile of the pyramid, and the second portal on the second tile.
As soon as the clot flies into the first portal and flies out of the second, immediately remove the portal (simply place it anywhere else) from the second tile. The energy bolt will hit the wall, fly back, and bounce off the inclined tile, landing directly on the receiver. This will activate the platform to your left.
Stand on it, and then you'll need to overcome several obstacles. The first is a horizontal pipe; simply duck to slide under it. Then there's a stationary platform; simply jump up and over it. Next, you'll see a closed hatch and a ledge in the wall to your left. As soon as the platform approaches the ledge, jump into it.
There's a button there; press it and return to the platform. While the hatch is open, place a portal on the other side of it, but not too far away, then jump back onto the ledge. Place a second portal on the wall and wait for the platform to reach the first portal. Then, jump into the portal to reach the platform.
After this, you'll see a ball of energy smashing between the walls of the tunnel you're traveling through. Again, you'll need to act quickly. Place a portal where the ball hits the wall. As soon as the ball hits it (and comes out somewhere behind you from the second portal), immediately move the second portal to another location so the ball doesn't hit it again.
Continue on. You'll see a slab half the width of the tunnel blocking the platform's path. Place one portal on the left wall, behind the slab, and the second on the slab itself. Once you hit the slab, wait for a large enough section of the platform to slide under it.
Then, jump into the portal on the slab to fly out of the portal on the side and land on the platform behind the slab. You'll be promised cake, but your platform will travel along a rail straight into the fire. To avoid this, wait until the platform exits the tunnel and immediately place a portal over the ledge ahead.
Place the second portal to your left or right on the wall, just below the platform, then immediately jump into it to reach the ledge. Congratulations, you've escaped death! Next, turn around—there's a very high wall behind you. Place the portal as high as possible, right up to the ceiling.
Place the second portal on the floor and jump into it. You'll fall out of the portal and fall downwards. You need to hit the portal on the floor again (or shoot it down again mid-flight). After that, you'll "go around again" and fly out of the portal at the top of the wall again, but with the momentum you've built up, this should be enough to reach the next ledge. Your escape has begun.
Portal 1 guide: (part 1) (part 2) (part 3)
Source: gamer.ru