Originally Posted by optics
So are you saying once you beat the game, it auto saves at the end which keeps you from playing any further for that campaign?
I'm at the part with the exploding dome room. I'm assuming that takes place before the lake, because after I did that scene, my next destination was above ground to the right. I didn't save after that dome scene because the dome room wasn't located in a place where I can accidentally go to and I was unsure if I was already at the end. Plus I still had one more piece of armor to get and X amount of items. At least this game doesn't require you to visit 100% of the map because just about every square above ground seems impossible to visit.
The game will save right before the lake (the explosive '!' mark is the save point). When you beat the game, reload, and you can continue from the lake edge and get the rest of the collectibles.
I edited the guide to better reflect this tidbit.