"I wonder if any of the other doors are still the same," Magnus says, thoughtfully. He opens the mushroom cave door, and it's still a mushroom cave, so he borrows Galahad's charcoal and writes 'mushrooms!!' on it. Then he opens the door to the giant's house, and it's a different giant's house: this time, Aegir's underwater banquet hall. He shuts that door firmly and scrawls an X on it.