I can't remember what it's called, or when it was released, but it involved two duplicate Earths located right next to each other, such that inhabitants of any given Earth, regardless of location, could always see the other one hovering directly above it (like a mirror image), and even journey from one Earth to the other.
And no, I'm not thinking of 2011's Another Earth. This was different.
And no, I'm not thinking of 2011's Another Earth. This was different.