I was curious if this was possible using the airwalk glitch. Can you explore it just like in the 'Home Invasion' mission or does it desync you if you try to enter the courtyard?
I tried it. The inaccessible roof of the palazzo is just like a regular roof, but inside the actual courtyard all the textures vanish. You can see through the walls to the street, and the ground is a static dark red, but you can't climb out or do anything in there.