The first time I entered the Choir Main Hall in Amnesia: The Dark Descent, my reaction was pretty much "Oh they don't expect me to go in there, do they? They do... Fuck this!"
For tose of you who haven't played the game, it's a huge open area that's filled with thick fog that makes it impossible to see more than a few meters away. And because it isn't darkness that limits visibility, the lantern doesn't help, and of course, there's monsters patrolling in there.
The basement area near the beginning of the game was pretty bad (in a good way), but the main hall was probably the "worst" area in the game.