To get glitch city you must have started out with turtwig and have beaten the story mode. Keep going to your house until your moms not there.tHEN go 2 sandgem into the lab and she will be there talk 2 herr and she will ask you if u want to help out herding some miltanks. say no and she will ask you again.press L1 7 times then go outside and go underground and go right back up. for some reason you will be in sunyshore city and it will be all glitchy.

DO NOT GO AND CRASH INTO ANY BUILDINGS OR GET ON YOUR BIKE BECAUSE YOUR GAME WILL FREEZE.
its weird but if you save while ur there and you turn your game on again, you will be at eterna city.