It was always so tense for me in all of the FF dungeons because it seemed any encounter could thwart all your time and effort, and it was back to the Inn you rested at. Finally getting Dejeon and Teleport was a huge relief.

Ice Cave was especially scary, but Citadel of Trials took the cake. That one group of enemies that kept casting Fira would pretty much decimate my party, so it was pure luck after multiple tries that I got through the dungeon only encountering maybe 1.