This is the forty-third level of the game, and takes place within Aperture Science Enrichment Sphere #5. This level requires the player to combine the effects of both Propulsion Gel and Repulsion Gel in order to proceed. Goo is present as the primary hazard.
Go along the catwalk and fire a portal on the wall. Shoot the other portal on the wall of the runway and go through the portal.
Fire the first portal on the floor under the Propulsion Gel and wait for the gel to paint the runway.
Then put the portal from the floor to the angled wall above the other portal. Place the other portal under the Repulsion Gel and wait for the gel to paint the surface.
Take the portal from under the gel pipe and place it at the end of the runway. Run from the other end of the runway through the portals and pick up the cube.
Jump down from the hanging platform to the platform below. Fire portals to the wall next to you and to the wall in front of the pipes. Take the cube with you as you go through the portal.
Shoot the portals to the floor in front of the button and to the floor under the Repulsion Gel.
Wait for the gel to paint the panel and then shoot a portal on the wall behind the button and the other one on a wall next to you. Pick up the cube and go through the portal.
Place the cube on the button and fire the other portal on the wall on the left, which is higher up.
Shoot the other portal at the end of the runway and go through the portal.
Go at the end of the runway and then run through the portal. Don't stop running until you are on the catwalk.
