How do I get inside the castle?

Hint 1 of 5:

You need to find another entrance.

Hint 2 of 5:

There's a clue in the Cave of Shifting Dreams.

Hint 3 of 5:

What other options are presented to you?

Hint 4 of 5:

Afraid to jump?

Hint 5 of 5:

Wearing your belt aren't you?