I'm sure we've had this topic not too long ago...
Anyway, I'll say here what I said wherever I said it. The worst dungeon, in my opinion, is Inside Jabu-Jabu's Belly. This dungeon disgusts me and I dread the thought of reaching it. I really don't like the premise for it and it's not even a fun dungeon anyway. The enemies are simply annoying, the layout is repetetive and the way everythign pulsates and wriggles turns my stomach.
I really, really do not appreciate being made to de-worm a giant fish.