Go to the Safari Zone and pay the P$500 to get in. Once inside, try going outside again. The attendant will ask if you really want to leave - say no and you'll be transported back inside. Save here, and do a hard reset. You'll now be able to exit without the attendant saying anything, so do that. Fly to Cinnabar Island, and surf up and down the coast until you get the usual Safari Zone message which tells you that "your safari game is over!", and you'll end up back inside the Safari Zone entrance. Exit this building (don't pay P$500 again) and you'll be in a very strange place.

It's basically a severely messed-up Fuchsia City. There are random tiles everywhere and sometimes you'll find that you have to Surf on what looks like land, or walk on water. You can't leave it without switching the GB off, so don't save here. When you're bored, just hard reset and finish the safari game you paid for in the normal way.