But which worlds have definitely been seen, mentioned, and hinted at? We've rounded them up here.
Our world. Obviously. Our world was a world without magic, until Mr. Gold (Robert Carlyle) brought magic here. It might not be the only magicless world, but it's the only one we know of for sure.
The Fairytale Land. The world which most of the characters come from, full of magic, fairy tale characters, and also some characters from legends, like Mulan (Jamie Chung) and Lancelot.
Wonderland. Wonderland appears to be much as we know it from Alice in Wonderland, full of bright colors, surrealism, an evil Queen of Hearts, and food that changes your size.
Neverland. Although we haven't seen it, we know that Captain Hook (Colin O’Donoghue) used a magic bean to go to Neverland, a land where no one ages. Presumably Peter Pan is there at some point, too.
Frankenstein's Land. We don't know much about Frankenstein's world other than it is a world without color (which is a nice nod to the original black and white Frankenstein film). We also know it's a world where the concept of science exists and is valued. However, it must have some magic, because Frankenstein is familiar with the concept, and Jefferson could travel to it, and apparently he can only travel to lands with magic.
Oz: In Season 2, Episode 5: “The Doctor,” Jefferson brought Rumplestiltskin (Robert Carlyle) a crystal ball, and told him the "slippers" he wanted from another land were no longer available. This seems to strongly suggest Oz, since Rumple said he wanted the slippers to get to the land without magic (presumably our world, to find his son Baelfire), and Dorothy uses slippers to get from Oz to our world inThe Wizard of Oz. Plus, we have seen a picture of flying monkeys in Henry's book...