C27 Last test(part III)

I saw that the box was opened a crack and the necklace was put back on. This necklace was my life. I can't be careless. He gently pushed open the lid of the box, inside were three keys and a note that read: "Congratulations, you have found the Phantom Fish's treasure. The treasure is at the bottom of the lake, you can just follow the map and search for it. There are three chests in the treasure