How do I open the vizier's trunk?

Hint 1 of 12:

You need a key to open the trunk.

Hint 2 of 12:

Specifically, you need something designed to open many locks.

Hint 3 of 12:

Such a key is called a skeleton key.

Hint 4 of 12:

One part of the game features several skeletons.

Hint 5 of 12:

You'll probably see it if you do anything wrong during the game.

Hint 6 of 12:

Where would you expect to find the dead?

Hint 7 of 12:

Try the Realm of the Dead.

Hint 8 of 12:

Look for someone who is carrying a key.

Hint 9 of 12:

He's at the entrance to the Underworld.

Hint 10 of 12:

Do you notice anything you can do on this screen?