"An immaculate box, securely locked. Makes no sound when shaken. What could be inside? Really valuable air?"
The Locked Box is a one-time salvage item that is found using the clues in the treasure rumor titled "Riddle of the Prince" in the player's notebook. It is found in Valka Castle, but it can be somewhat tricky to find if the player does not know where to look, as it is on top of the awning over the throne in the Mermaid's Ballroom.
The appraisal reward for finding this item is 9,500 pelagos.