After you collect the Compass, make your way back out of this room. Head
through the west door, then climb out the window to reach the courtyard
again. Become a wolf and defeat the white wolves that may have reappeared,
then look on your map for the chest in the northeast area of this room. Walk
over it and you will be prompted to dig, so do so to reveal a chest. Dig
twice, then open the chest to receive a Small Key.
With the key in hand, turn back into a human and unlock the east door. In
that room, you will find 3 cannonballs. First, grab the lever on the wall,
then place a cannonball in the lowered slot. Go through the door again and
pull the lever on the other side to slide the cannonball down to the other
side. Pick it up and bring it over to the cannon, and insert it. Push the
cannon so it faces north, then drop a bomb inside and launch the cannonball
right into that ice creature, destroying it. Now you can access the north
room, so head into that room now.