The Legend of Zelda: Twilight Princess HD Tips

Secret room in Hyrule Castle
In that courtyard on the west side of the castle, go to the place with the triforce engraving in the ground with the 6 pillars (the ones where you need the Gale Boomarang to activate the door). On the left side, there is a pile of leafs. Get into wolf form and dig under there. Then you will get to the graveyard of the castle, which holds the key to the treasure room of the dunguen and a few other treasure chests.