There's been a lot of debate on where Hyrule ends and Termina begins. Personally, I think its at the point where Skull Kid turns Link into a Deku Scrub. When you leave that room, the world feels more... Termina-ish. I know that sounds weird, but in playing OoT and MM, Hyrule and Termina have distinctly different atmospheres.

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Caress the one, the never fading rain in your heart- the tears of snow-white sorrow.
Caress the one, the hiding amaranth in a land of the daybreak.