Take the cube over to the drop-off point on the other ledge and head through another green portal. Press the red button on the right side to receive a cube.This will lift the four tiles the player is standing on to a previously inaccessible ledge. While standing on this piece of flooring, turn to face the cone on the floor and place the green portal on the wall behind it to activate the cone.Walk over to the outlined square on the floor near the wall that players face when they first enter the room. Go through the green portal again to the working room to see that the portal has not moved in this dimension.This will activate the cone on the floor in this dimension/ Head through the green portal once more and create another one of the orange oval-shaped portals on the wall opposite the right-hand window inside the left room.This will activate the receptor on the opposing wall. Above the window to the right of the blue miasma doorway, create a secondary orange oval-shaped portal.Create another green portal outside of the room to head back into the previous timeline where everything is working.

Create a green portal anywhere in this room to leave it in the other timeline.Place an oval-shaped portal at the left end of this room for the laser to shoot into.After entering Chamber 15, head through the blue miasma door on the left.For Chamber 15 in particular, there are quite a few steps but with minimal use of the third green portal.

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