Player 1: Upon entering the main chamber, look for the start of the excursion funnel in the top left-hand corner of the room. Get a portal up on the horizontal panel hanging down above it, then look to your right and on the ground (near the stairs), there’s another horizontal panel here that you need to place your other portal on. This’ll create a funnel that extends up to the ceiling.
Player 1: Stand on the red button on the floor and this’ll lower a vertical barrier from the roof above. Now look to the left-hand wall and you should notice a single vertical wall panel jutting out from the wall. Fire your exit portal here (so the excursion funnel is now running horizontal from left to right, across the room). This in turn will cause player 2 to drop like a stone.
Player 2: You need to react quickly once you start to fall, so as soon as player 1 removes the portal from underneath you, aim directly at the panel below you and set your entrance portal here, this’ll cause you to fly out of the angled panel, hit the lowered barrier and fall into the funnel, taking you right over to the platform by the exit. Now, pick up the Companion Cube waiting patiently for you up here, drop down to the lower level and make your way over to the red button on the floor where you need to set the Cube on.
Player 1: Once the Cube is on its resting place, reset your exit portal so the funnel is once again coming out of the horizontal panel on the ground (allowing you to jump in and ‘float’ up to the ceiling). Ask player 2 to join you afterwards so you’re both in the same excursion funnel at the same time. Once you’re both ready, look back towards the wall ahead of you and place the portal on the vertical wall panel (once again creating a horizontal funnel moving towards the exit). This’ll immediately cause you both to drop towards the ground. Player 2: As soon as you’re both hurtling downwards, very quickly place an entrance portal below you, allowing you both to hot the barrier, drop into the funnel and get carried over towards the exit!