The FOR WHAT!? achievent is earned by finding a secret area inside Level 17.




First, complete most of the level by turning off the lasers and avoiding the spinning blades.
Head up towards the door, being careful NOT to go through.




Once you are by the door, invert the gravity so you are standing on the ground above the door.
Walk right above the door towards the edge of the level.




Ta-da! You've now stumbled upon the secret area!
Head towards the turtle until you come across a dog.




Be sure to stand just to the left of the dog so that when you invert the gravity, you don't fly off the screen. I died the first time I did this by standing on bed/chest/whatever that is.
Invert gravity.




You'll now be standing on a floating platform. Carefully walk to the edge and head for the switch.




Once you hit the switch, say goodbye to the dog and watch as he gets sucked up into beam.
Viola! You are now the proud owner of the FOR WHAT!? achievement.
Walk through the door and you will be transported to a previous level. Simply exit to the menu and continue on your journey to complete every level.



Thanks for reading and I hope this guide was helpful!