Oh man, I could go on forever with a topic like this.

FF2: The whole Jade Passage -> End of game sequence, nothing less then like 12 bosses along with hard as hell (no pun intended) random regular battles. In fact, there were a lot of places like this in game, most of the final dungeons.hell, every dungeon in FF2 sucks, there I've said it.

FF3: Styx Tower, Dark World, Dark Knight Cave all ring bells to me. Styx Tower is a "point of no return" so be prepared or get buried. Dark World is the same, except even worse because the bosses are a massive jump in difficulty and if you're not stocked up then you will die no problem. DK Cave sucks because every time you physically hit a monster, (unless you are using the DK class which it sucks at best) they multiply and become an ever-increasing threat.

FF4: Tower of Bab-il, lots of bosses, boring overused dungeon with same layout from Barbaricca's dungeon, FuSoYa being a useless character, etc.

FF5: Most of it.

FF6: Zozo, Magic Tower, Hidon Cave, Magitek Factory, Phoenix Cave...

FF7: That stupid jungle that I hated because it had to do with frogs and flies and it was annoying.

FF8: the Time Compression World. Seriously this game is stupid hard to follow at the end, I hate it.

FF9: when the world gets swallowed up in the mist and my dumbass waits until disc 4 to do all the chocobo sidequests

FF10: Though I wasn't a big fan of the game, I did like all the different areas that Tidus and crew travelled through, so kudos for SE to not make an area I hate in one game.

Any SMT game in any dungeon: *shudders* I swear I would rather play all of FF2 over again instead of doing any of these dungeons, theres only so many blind rooms/curse rooms/ warp rooms/no magic rooms/**** you rooms/etc that I can take before going crazy.