Sidenote - Why do I have to play this and where did it come from? : There was a voiceline from Duke about the oldest melody, which is Hurrian Hymn No. You'll know if you did it correctly because the saving icon will be displayed in the bottom left. The image below displays what keys need to be hit. You will need to shoot a series of keys in correct order. Now proceed to Scarface's room, and walk over to his piano. It will assemble into a floating mess that is constantly spinning. A bunch of pieces will be laid out, and you should have the option to assemble it.
Now head to the kitchen and use the medalion to open the three boxes on the table. Then you need to go to Duke's desk and pick up the Medalion. Once you have those hiests completed, enter your safehouse.
