I think that the hardest dungeon of the series is the Spirit Temple in The Legend of Zelda: Ocarina of time Master Quest 3D.. almost illogical level design!! MUST difficulty!
YOUR land... New Hyrule...
"Ah, but child... That land will not be Hyrule. It will be YOUR land!"
~ Daphnes Nohansen Hyrule (King of Red Lions) from The Legend of Zelda: The Wind Waker (GameCube)