What Lies in the Multiverse

During chapter 2, you'll repeatedly have to extend a bridge or open a door for Everett so he can progress. One of these times, a short way into solving the puzzle to open the door for him, Everett will tell you not to bother because he's found a shortcut. At this point you can just go the way Everett did to progress, but if you continue solving the puzzle to open the other way forward, you'll unlock this achievement.