I see. There is going to be a stage in the middle of it that probably goes down the long tunnel
All'a those images come from Sakurai's Miiverse. In which the image's origins are explained.
The image is apparently part'a the Pyrosphere "that's really not visible in-game."
No, I think it's just in the background, considering we already know what the Pyrosphere looks like. It's the Ridley boss area.
It's like the good ol' days with the Smash Dojo. T'is good marketing too, leavin' your fans without entertainment for too long kills the hype.
... Not that hype for Smash will ever die. Look at Melee for 'Karp's sake.