Portal 2

This is found on Excursion Funnels: Chamber 9 in co-op mode.

Easily done split screen with two controllers but way more fun with a partner.

Not my video props to the guy who made it.

Edit: Video Removed. Read comments for more information. I am sincerely sorry.

Course 4: Excursion Funnels Chamber 9.

Note: Going for this achievement means certain death

The Companion Cube is right before the end of the Chamber. Continue playing the chamber normally until you have to use the Hard-Light Bridge to knock the turrets off balance so you can make your way across safely. On the opposite side of where you would lay the portal to do that is a tunnel that goes to nowhere. You will want to lay your Hard-Light Bridge close enough so that it will continue down that tunnel. It would be best to do this while you are in the Excursion Funnel against the wall and you can't move. Now once you have your Hard-Light Bridge placed properly have the other person shoot their Excursion Funnel below so you fall into the Excursion Funnel and glide your war to the Hard-Light Bridge. Now you will be pinned against the Hard-Light Bridge. Have the person with the Excursion Funnel shoot their portal right to the left where the Hard Light Bridge portal is. You will no go down the tunnel and if you look at the wall to your left (facing the direction you're going) you will see the wall open up and reveal the Companion Cube and the achievement will unlock.

Where - Area 4, Chamber 9

How to: Complete the whole area up until you need to insert the disc, once you get to that part walk into the room and back out, all the turrets will be gone, and you can work your way over to this, after you have completed up until the disc area, kill yourself. Yes you read that correctly, jump off the ledge.

Now redo the whole portion again, but this time while traveling over to the disc area look to the left (If you are facing the disc area) and you will see a White wall that you can place your portals on, have the person controlling the light bridge place one after the support beam, it should now be blocking your path to the insert disc room.

Now once that is done float in the tunnel till you are both against the light bridge and have the person controlling the tunnel shoot it at the same wall the light bridge is coming from, if done correctly you should both be floating into a dark area, the person controlling the light bridge can shoot it elsewhere to get it out of the way or shoot their other color to completely get rid of it, you will float in the tunnel until you come to a room in the wall that is windowed off and has a Companion Cube in it, this is where the achievement should unlock for you guys.

Thats it, it seems long but its really quite easy, oh and you will die after seeing the cube. Seriously, there is a spike wall that you can't avoid.