What is the mysterious box?
Solution 1:
This chest is Stone Coffer. After you upgraded to Stone Castle, it will appear. Every gem stored there will be avaliable between islands if you pay 1 gold to the NPC next to it per gem.
This chest is Stone Coffer. After you upgraded to Stone Castle, it will appear. Every gem stored there will be avaliable between islands if you pay 1 gold to the NPC next to it per gem.