Admittedly, this is just an old idea I had for an Unova stage... But after seeing some recent Pokemon ideas I thought a more iconic location would work nicely. Castelia is known for being the most prominent city in the Unova region, being modeled after New York City. It is the second largest city in any Pokemon game as well (Lumiose exists).
This is the old sketch I had of the layout:
Essentially it's the 4 docks at the south end of the city. Sometimes the Royal Unova could dock, adding an extra platform. The main thing, of course, is the sprawling city in the background.
I also did some work in a music write program for this a long time ago, too...
It's just a midi file, but you get the idea... combines the music of Skyarrow Bridge and Castelia.