The first place i found to do this was on Antarctic's 5th level, it's pretty hard to describe where to do it, so just check out the video below :)
But when you get there, tap A to jump up each one, don't even think about touching your analog sticks because it makes you jump off at a dodgy angle instead off onto the next wall.
Credit to Nod Nolan for this:
This will be easier once you've got the 'Alternate Route' achievement, you obviously do this by pressing X on the map then buying the split route.
he also says
"hanging from a platform is your friend. Hang at the top of a column of walls then drop down to the next level, until you reach the bottom wall. Drop down one last time so you start sliding down the bottom most wall and then start jumping your way back up again."
If you're going to give me negative feedback, at least comment why.