The most sci-fi looking city or locale in the world?

Name a place where the architecture is so far-out that you could use
it as a sci-fi set.
I think Lucas's use of actual locales in THX was brilliant. 

And, which natural terrain on Earth looks most extra-terrestial? I saw
a documentary on the volcanos of Kilmanjaro where plants and the
geological formations were truly out of this world.