Go to the Core level (The dark area with the parkour and the bathroom) because it increases the chance to get the achievement to 50%.
Stay there with your game unpaused and just wait, it should take 6-8 minutes if you are lucky.

The sequence that you should complete the parkour in is normal jump, normal jump, normal jump, shift jump, normal jump, normal jump.
If you end up falling then quickly press alt+f4 to force your game to shut down so that it doesn't save.