Shipwreck Layer 17 Music Box
In order to get past the Music Box in Layer 17 of the Shipwreck dungeon (located off Queens) you must complete the Fortune Teller's house and have your fortune told by her. You have a few different options to choose, the proper one is "What happened to the man whom the queen loved?" from the story the priest told you at the Cathedral. The fortune teller lady will jump on your head (weird, I know) and you'll have a short cutscene where you see Rando's shop.
Head over to his shop and examine the counter for a key which is required to unlock the Music Box. After acquiring the key I highly recommend you stock up on healing items/a few repair powders as you're about to fight a boss upon opening the music box. I guess you probably already figured that, but why not give you a heads up just incase!! If you would like a strategy for the boss, keep reading past the picture...
Scroll for the boss.....
The boss you are about to fight is an Ice Queen, she will primarily use ice attacks against you and the "real" strategy is to use Toan or Gordo to knock down her shield, then use Ruby to damage her. You can only use Ruby to damage her once her shield is down with the Fire element on her Ring. Also, you can only damage the shield with Toan, Gordo or Xiao.
What I did for the fight is I used Xiao to damage the shield until it was gone and each time she shot ice at me I ducked behind a pillar, only popping out to shoot 3 or 4 times to take down her shield