Right at the beginning, you will have to choose whether to go left or right. This will determine which way around you will go around the tunnel one and a half times. After you have made that decision, everything else is pretty straight forward. Keep jumping either to the left or right (it should be in the same direction as your first move) and after 6 gravity switches, the achievement will be all yours.
The Runner and Lizard are good characters to use as their good maneuverability can help you make sharp turns to the left or right when necessary. The Pastafarian also works because if you miss a platform, the her light bridge will be able to save you. You can abuse this and just jump for nothingness and still get the achievement, because the Pastafarian's bridge is so strong now after the revamp that most of the tunnel is usually covered in bridge.
Keep in mind that most of this achievement's difficulty comes from the rarity of the level. Don't feel disheartened when you can't find the level, as you shouldn't have too much trouble getting the achievement (once you find the level) if you have a good character.