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Actually, I don't understand where you got stuck. On the second island, you get the Guardian's Shield after removing the wall and saying the password. Also, on the second island, there is a descent into the underground, where you need to go using only the arrow keys. I won't tell you what happens next.)
I've completed the entire underground, saved the princess, and assembled the catapults; in fact, I destroyed the castle in this underground.
But I'm stuck near the last statue; I still don't understand where to enter the password.
Here are the screenshots. The first one shows where I'm stuck (screenshot "passage"); maybe it's not the right wall that disappeared. The other two are from the underground.