Wow, I went exploring the Hyrule Field, the ruins off Castle Town and Hyrule Castle itself yesterday because I hadn't done that yet. I didn't go to Ganon himself though, but I did peak into the great Hall on top. Got up there with my crappy gear so I figured there's no chance anyway. Hyrule Castle especially is a totally epic part of the game, and a treasure trove of awesome stuff. I love the music there, a mix of Zelda's Lullaby and Ganondorf's Theme.
To do a bit of theorizing;
This whole central part of Hyrule obviously mixes parts of Ocarina of Time and Twilight Princess. The castle itself is the one from Twilight Princess with it's towering spires and bridges and the hall on top. There's the dungeon and sewers where you play as a Wolf in Twilight Princess for the time and even ruins of the large winding staircase towards Zelda's bedroom.
In Hyrule Field, the Arena though in the wrong place is largely reminiscent of the Arbiter's Grounds from Twilight Princess. More importantly, the Abandoned Farm (or whatever you call it, this is at least the Dutch name for it), is a ruined Lon Lon Ranch from Ocarina of Time. Everything's there where it should be; a ruined barn and brick building on opposite sides of a path on the north end, which were the house and the barn with the cows. The brick tower to the south, where there was a small block-puzzle to find a Piece of Heart in Ocarina of Time and even the small shelter beside the horse field that had a Gold Skulltula on the side of it. The oval shaped horse field is obvious, parts of the surrounding fences and the gate are still there. Even the race track around it is slightly visible. Such a sad moment to see it all in ruins now.
Lastly Castle Town, which is a mix of both the Ocarina and Twilight versions. The Market Square with the large fountain as well as the lead up towards the gates of the Castle is Twilight Princess's. Then there's an Ocarina influence with an area called Ruins of the Hyrule Cathedral on the eastern edge. Not coincidentally is this exactly the spot where the Temple of Time is in Ocarina of Time's Castle Town. This kind of retcons an inconsistency between Ocarina of Time and basically ever other Zelda game; Ocarina's Temple of Time can't be the real Temple of Time, because it's supposed to be in a forest down south, according to A Link to the Past (though there it's forest isn't in the south), Twilight Princess, Skyward Sword and now Breath of the Wild.
Anyway. Naturally the place is crawling with Guardians, which are terrifying. I especially hate the Turret ones in the castle, they're everywhere. Not as terrifying as the Lynels though, everyone of them are total Legolasses. That white one, what.
But yeah wow, as a Zelda fan, totally in awe, and I spent hours looking around all those places.