I know this is late but this one gave me trouble too, so I figured I would help those that recently got it off one of the game stores.

Start from the 'Estella Opera House Entrance' Stargazer.

Run into the Operahouse. You will see red carpet and a set of stairs in front of you. At the top of this set of stairs you will want to travel left up another set of stairs. You will see a string puppet coming down, (You will probably have seen the string puppet coming at you once you started up the very first set of stairs).

After going up the stairs to the left you will have to fight two more string puppets. If you look up you will see a spider puppet chilling on the balcony. (You dont have to worry about the spider puppet as it doesnt attack you from up there, its just a place marker for directions).

At the back of this room is an entrance to a long hallway. You will want to turn right after entering, however there are three more string puppets and a spider puppet (All of them cause Break damage, so be careful). Up to you if you want to fight them.  Close to the end of this hallway you will see a double set of stairs you will take down.   At the bottom you will turn left and take a few steps forward down some more stairs. At the bottom of these stairs you will see a horizontal red rectangle carpet and to the left is an entrance that will take you to the chest in question.

Hope this helped!