So the question is, if you had the most expensive house in the world, would you advertise it?
Maybe not, which is why it's hard to say what house properly holds that title. But if you're curious to see what one of the contenders looks like, check out Updown Court, the British estate of the Crown Prince of Dubai, who apparently has a little cash to spend. The house has got 3.5 acres...of marble, for chrissakes.
Unlike other "most expensive houses in the world," this one actually has a video tour of the interior and a narrated explanation of the amenities; and while the house is a couple years old, well, it's the only look many of us will get at how the other 0.00001% lives.