Warnings Active: Cube Dispenser, Cube Hitting Head, Orb Hitting Body, Orb Receiver, Dangerous Water, Jumping Into Portal, Flying Out Of Portal, Turrets, Don't Drink The Water (all except Cake, basically)

Shoot a portal across the way (onto the ceiling on the next platform) and then make a portal within reach (the hallway behind you works for this). While you are falling out of the ceiling portal, shoot a portal onto the third platform (or shoot at the ceiling above it, if you miss it while falling) and then make a portal on the wall near the one you are standing on (the wall that is across some water and is actually the wall of the third platform). Make the wall portal lower than your eye level, as you will be jumping down into it. On this third platform, look across to see the fourth platform and do the "one on the ceiling, the other on the floor" thing again. Look over at the fifth platform (marked with a four-dot icon, because it doesn't count the first one). Make a portal on the jutting-out section of wall and then another on your platform. Keep the portal on the jutting section active and move the floor portal to the pit. Jump in and launch yourself over the gap. Now you should be at the button; ignore it for now.

Walk forward and press the smaller button. Use the section of wall that was pushed out as cover so the turrets don't shoot you. Now we have to get rid of those turrets; luckily, we have two kinds of markers for destroying these. Place one portal on a scorch mark on the walls, and another at a wall with a laser sight on it (from the turrets). With luck, the orb will go through (it may take some time, as the emitter is rotating like the portal guns earlier did) and smash the turret. Repeat this for all four turrets. With those neutralized, we are free to attempt to activate the receiver.

Look across the way and notice the jutting-out section of wall. Make one portal there and another on any of the scorch marks. Once the orb has passed through the portal (and immediately afterwards) look to your right and notice the thin piece of wall sticking out of the wall facing the small button. Make one portal within reach and the other on that wall part. Jump through and press the button. You must time it so that the button is pressed before the orb hits the hatch. If you miss, simply move closer to the button to speed up the process (you will have to send the orb through the portals again before you press the button though). If you did it correctly, the platform in the middle should be active. However, the portal does not go all the way to the cube. Jump down and land in the lower area. Before you press the button, make a portal on the wall behind you. Then make another back in the area where you began. Press the button and go through the portal (you may need to make another if you put it on the section of wall that comes out). Once the section of wall is out and angled, make one portal on it and then go to the right of the way you came in and look down to see a pit. Make another portal in the pit and launch yourself across to the cube. When the moving platform comes back, jump onto it with the cube (the area is elevated, which is why you are able to make the distance). Cross the gap, leave the cube, and then go back to the button. Again, set up portals before you open the button. Once the button is pressed, go through the portal to return to the other side, grab your cube, and go through the open space. Return to put the cube on the button and proceed onwards (make one portal on the floor near the door and the other on the pit, as the platform with the button is un-portal-able).

In the next part, we are shown several elevated platforms and one pit. Make a portal on the first platform, and another in the pit. Jump into the pit, and while in midair make a portal on the second platform. Repeat this for every platform until the last angled one; if you can keep it going, your momentum should allow you to make this in one run. If not, keep one portal static on the platform that you reached and put the other back down at the bottom. Once through, move the second portal to the bottom of the pit and resume from where you were. Finally, go into the elevator to reach the final testchamber.

Portal Walkthrough