How can I open the locked chest in the east tower

Hint 1 of 4:

Watch your step on the stairway, it's a bit tricky.

Hint 2 of 4:

Did you check in the coffin before Dracula arrived?

Hint 3 of 4:

You should have found a regular, non-magic key.

Hint 4 of 4:

Open the chest to get more goodies.