As Sonic in Story or Trial mode, choose the Silver Boss battle. Get as many rings as possible (fifteen), then go to the alley in the corner. Get as far into the corner as possible. When Silver uses his levitation technique, try to get back in the corner. Silver will use the levitation technique again and the rings will be behind you. You should be able to collect the rings before hitting the wall and dieing. Then, when you hit the wall, try collecting your rings. You will then go outside the level's boundary. You will be able to walk on invisible bridges and hit other invisible things. Silver might even also get out of the level boundary and throw you out of Soleona, causing you to keep flying forever.