The conclusion of The Sure Bet King took place at a Los Angeles super-mansion. My current WIP is also focused around a super-mansion. The super-mansion is one of those setting places that I just love. They’re (impractically) big, they can have a lot of stuff, and they can have very different themes.
The closest thing to an official definition of a “mansion” is “a luxury home at least 5,000 square feet in size”. Super-mansions are even more nebulous, with their only real distinguishing feature being their bulk. My own definition is “it’s a super-mansion if any one room in it is bigger than an entire normal mansion”.