On the road opposite Bondi Beach (Campbell Parade) there are several blocks of flats dating back to (my guess) the first two or three decades of the 20th Century. And each of them is titled "Something or Other Mansions".
Now while the real estate under these flats would probably cost about the same as the debt of a third world country... this old fashioned building with a humungous crack in the front of it really isn't my idea of a "mansion".
However the description may not be as absurd as it first appears but rather the result of yet another absurd quirk in the English language. There is in fact, according to Oxford University Press, something called a "Mansion Block"
"noun Brit. a large block of flats."
It's certainly a term that I doubt you'll hear outside of Britain, but back in the earlier half of the 20th Century Australia would have followed British trends pretty slavishly.
So I'd still rate it as weird... just not, perhaps, weird in the way that I thought it was when I first saw the buildings.