One Piece

It's the legendary MacGuffin. It is an abstract concept of that which is far away and you must get, and it is, by definition, impossible to talk much in specifics about it, only in general terms. It is quite a powerful thing even if it has no physical shape. It is, however, similar to Schrödinger's cat, since as you approach the point when you can see it, it stops being what it is, and it starts being something else as its form, position and nature collapse into a physical state, its nature permanently changed, and its enormity reduced into a single point of excited disappointment as the story ends.