Paul Zap191,536 Locked 27 May 2013 13 Dec 2014
The achievement pops when you get to Cauldron Lake and there's a short cutscene, specifically at the point of the "Wheels Within Wheels" achievement.
General anecdotal advice for this achievement: I played through on Normal, not looking out for collectibles and taking my time, I didn't get the achievement on Normal. Then, I played through on Hard, while making sure to get every single collectible, still didn't get the achievement.
Then, I played through on Nightmare, getting every single Nightmare mode manuscript page along the way, including in this section. I even didn't bother trying for this achievement. I took my time, but having gained knowledge of the level from my Normal and Hard playthroughs, I went through it relatively smoothly and quickly. I even stopped completely for the day, shutting down my Xbox and everything. Then I continued the next day, dying a few times and going out of my way to get Nightmare mode manuscript pages, as well as not really avoiding any fight (but certainly not going to find the unnecessary ones), and I was surprised when the achievement popped. It really wasn't that difficult to be honest.
An important tip is that if you're going for collectibles, like I was, then grab them, and afterwards restart the checkpoint; the collectibles are saved through that (even though you can still pick up manuscript pages after you've found them before, they are still unlocked even if you choose not to pick them up because you did so before).
Good luck! If I can do it on Nightmare difficulty while taking my time and getting collectibles, anyone can do it on Normal difficulty without trying for collectibles and actually trying to go quickly.