Narnia, Zelda, or Pokemon.
Narnia is absolutely an amazing universe to live in, if you've read the books you know exactly what I mean. And as a bonus, you could live an entire lifetime in Narnia, then come back to the real world and almost no time's gone by at all! Hell yes. Only problem is you can only go to Narnia three times before your turn is up.
Zelda has all sorts of amazing things, especially during the times of peace after Link has done away with the evil. Have you beaten Ocarina? Do you remember the happiness and celebration after that? The world was good. Gimme some of Link's badass tools and some transformation masks and I'm good for life.
Pokemon is awesome because, let's face it, if a 10-year-old can get by OK on his own and have totally badass pets along the way, that's definitely a world for me.
Runners up: Star Trek, Harry Potter, Star Wars.