You have to go back to your house in hateno village, then jump in the well behind your house. you will find a cave with zelda diary in it telling you the exact location. but if you don't want to do that, 7lue65.jpg (click to show)

Use the lookout landing tower to launch yourself to the castle. Bring stamina restoration meals and tulins vow to get to ensure you will get to the castle without running out of stamina when gliding towards it

you can also get the champions tunic (from botw)by getting all the bartering statues

I did that but it took me a while.