The Ten Worlds
There have been ten worlds mentioned in New Century so far.
Earth: This was the New Century timeline up until the divergence of 1872. Our Earth, where history proceeded differently, has never been mentioned, aside from in speculation during Secret Rooms.
Centrum: First appearance; The Cartographer's Handbook. This is the main version of Earth featured in New Century, and maybe the most important. As of Phase 1 it is eleven years displaced from the regular Earth timeline, and every portal that has opened on this planet's surface further changes historical events. The world was named by the wizard Merlene at the prologue to The Princess Thieves.
Rama: First appearance; Tiger's Eye. Several million years ago, rather than apes touching that monolith and evolving into the dominant species, it was neolithic lions. Cut to 1883 and evolved great cats inhabit the globe. There are legends spoken of within the tribe which Hrao belongs to, of a more advanced society which existed in recent times on the western continent, but the ruins she encounters later in the story are apparently all that is left of that civilisation.
Celador: First appearance; The Princess Thieves. This is the version of our planet that the Duart species were living in before the portal opened into Centrum's London.The Duart have their own history, involving conflict with a monstrous, fire-breathing species called the Drakes. They also have their own, much more recent, Arthur legend.
Hannoth: First appearance; The Princess Thieves. The world that the enormous Akka species made their exodus from. They first took refuge in Celador in return for lending their aid to the Duart, to drive away the Drakes. Then a few decades later they made the trip along with their diminutive neighbours, through to Centrum and their version of London. The doorways to Hannoth have been closed for a long time, so there is no going back to their home world.
There are five other worlds/timelines which have not yet been named. Some are accessible through portals found in Centrum.