When it comes to dungeon difficulty, one thing will always cause blood-boiling fury: confusing, maze-like design. The Nortune's D-Block Sewers begins with a murder mystery, and ends with players vowing to never traverse another sewer. The area is dark and dank, and you're bound to get lost when everything looks the same.
Fei and his team don't exactly have a map on hand, so it's easy to get turned around. Oh, and the area is full of poisonous frogs ready to whittle away your valuable hit points. If the tough enemies weren't enough, one of the hardest bosses in the game, Redrum, makes it a chore. When a boss can poison, confuse, and steal life to add to his own, you're in for a rough time. Hanging up your coat and calling it a day wouldn't make you a quitter--it would make you wise.