As I understand it, the Dark World in
aLttP is the Sacred Realm after it has been infiltrated by Ganon.
I haven't played Twilight Princess, but it would make sense if the Twilight Realm were the intermediate stage between the Sacred Realm and the Dark World.
Is there anything in
TP that contradicts this?
Some more evidence in favour of my theory:
In
aLttP, if you enter the Dark World you turn into an animal or something strange, that is if you don't carry the Moon Pearl. In
TP, Link turns into a wolf whenever he enters the Twilight Realm, whereas in
aLttP his descendent turns into a rabbit. Perhaps the reason Ganondorf first became a giant pig man was that he crossed the border between the Light World and the Sacred Realm.