My Favoritest Story Setting

First things first ... yes, I'm fully aware that favoritest is not a real word.  Now that that's out the way, we can on to the topic at hand.  Story setting.  Some writers like to use the same setting for each book or story; usually this is because the books are in a series (like the Harry Potter series) and sometimes its a shared setting for all the (not necessarily related) books that they write (Terry Pratchett's Discworld is like this).  Some writers like to make up their own world, essentially giving them full control over all the details, without needing everything to make realistic sense.  Others (I'm firmly in this camp) like to use the real world as the backdrop for their stories, because you and I and everyone else knows how things work in the real world.

Or at least in theory we know how they work.

Tell us about your favorite writ­ing project/universe that you’ve worked with and why.
My favorite project/universe/setting that I've worked with is alternate Earth, where almost everything is exactly like what you or I or anyone else knows.  There's just a few changes sprinkled in to make it fantastical.  Just about every horror book, thriller, or heck most non-genre fiction uses this type of setting (usually without the obvious fantastical elements).

In the past, I've tried to come up with complete alternate world settings, but they always felt hollow and incomplete.  Now, I like to do what I, for lack of knowing the correct term, call "world within world".  Think Harry Potter.  The outside, every day world is pretty much what you or I experience on a day-to-day basis.  However, hidden just beyond the periphery is a secret world of magic.  Or monsters.  Or sparkly vampires.  Or unicorns.  It doesn't matter what lays beyond, just that something does.

And, into this hidden world the characters are thrust and now have to cope with learning the "truth" of their reality.  It's the act of uncovering all that "truthiness" that I find interesting.  It's also, conveniently, where the drama is as well as all that tasty character growth and other literary terms.

Now, do I wish that I had created some sort of wondrously complex and detailed world like Tolkein' s Middle Earth, or Pratchett's Discworld?  Of course I do.  At the same time, however, being able to say "Meanwhile, on the Upper East Side" and have readers instantly know what I'm talking about is worth it's weight in literary gold.

Someday I do intend to fully flesh out and develop a completely "my own" world setting.  But for now, I'm content with using a world with the world.

Is there a particular story setting or world that you like to write apart?  A favorite that you like reading more about?