How do I get into the castle?

Hint 1 of 5:

You should ask the wise Soka for help.  See the previous question to find
out how to talk to him.

Hint 2 of 5:

He'll tell you not to go through the front door (W).

Hint 3 of 5:

And he'll say that you need to use the sand of time on the trenches.

Hint 4 of 5:

Can you think of any time piece that uses sand in it?