It's an interesting thought and entirely possible! Personally speaking, I really like the idea of the entire thing being a hotel with themed wings, but it really could go either way
Thanks, I decided to expand on it since you seemed to think it might be the case.
So each "mansion" is stacked onto the previous one. And they each have a theme and a particular design/coloring. This is what I've put together.
This is the image I'm working from, for reference:
Okay:
Hotel: This is the base, and all of the footage we've seen so far has taken place here. The square stone structure at the top is part of the hotel, not the castle, since it shares the same coloring. Maybe it's a boss room, maybe it's the concert hall as GX suggested. Who knows. But it's not part of the castle section, it sits "in front of" the castle section.
Castle: This sits behind the big stone square and actually includes the greenhouse/garden area. It seems to extend up behind the green lettering a bit obscuring some of the structure, so we can't exactly see where this ends and the next section begins.
Office: I'm calling this an office building, but I have absolutely no idea what it will be. From the top section it looks a bit like a skyscraper with a design on the face of it, so I'm just treating it like an office building. Again it's hard to tell where this begins and the castle ends but I think I've cropped it at around the right place.
Diner: I'm calling this a diner because the angled portion on the left looks a lot like the back of a sign on a 50's style diner:
I could be 100% wrong on this but that's what I first thought when I saw it. Maybe it'll be "50s-futuristic" themed.
Zuul's House: This looks a lot like the top of the building from the first Ghostbusters movie so I'm calling it Zuul's house. I'm guessing this is the final area (duh) with the final boss fight, which, as GX suggested, is probably King Boo.
-----
So yeah it seems pretty clear to me that these are all different mansions stacked on top of each other. Presumably sharing a common elevator shaft, but beyond that I'm guessing they're all discrete locations with completely different themes and architecture.