This chamber is the prelude to the final puzzle in this chapter (a behemoth series of puzzles). Your objective is to reach the final chamber at the top of this room, and this is how you do it…
From the floor, aim up at one of the pillars high up, so you'll land on the metal girder once you step through. Turn to face the wall with the door and fire a portal onto the slanted wall above the door.
Now set a portal on the ground far below you and then fall down into it. You should sail through the portal above the door, onto the blue gel and you'll find yourself being bounced up to the next tier of the platform.
At the back of this section there’s a light wall panel on the floor, so set a portal here, drop down a level and then once again drop down towards the ground, through a portal and you’ll sail up into the air, overlooking a large shoot-able section of floor on the top-tier.
Shoot a portal into the floor, and as you fall, place a portal by your feet. You can now step into the top portion of the room.