Les Plusieurs Mondes is a name generally given to the 108 individual worlds arising out of the magical aether of creation. Literally translated as "Many Worlds", in this context reference made to a "world" or "realm" does not imply a single planet or geographic region, but an entire universe or plane of existence.
Worlds coexist side-by-side with each other, separated by the Thaumatadiastasis, a plane of reality that can only be described as one of pure magic.
Theorized Structure of the Multiverse
Most researchers of les Plusieurs Mondes agree that each of the known universes is part of a fractal chain of branching timelines, they are still divided on the number of individual seed universes.
In the lore of the Wizards who have controlled the Tower over the various aeons, it is conjectured that there are in fact only 108 existing seed universes, the number of individual worlds discovered so far.
Others believe that due to the infinite number of alternate timelines, there must in turn be an infinite number of seed universes.
Still others claim there is only one seed universe and that each of the 108 worlds of les Plusieurs Mondes is tied to a different super-aeon, defined as the period of time between a universal big bang and big crunch. They argue that as the Thaumatadiastasis exists beyond space and time, it must in turn touch all points of each.
Travel Between Worlds
The Wizard's Tower is not the only method of travel between worlds.
Travel between all the fractal timeline emanations is capable through the manipulation of Physics, and has been achieved in a number of non-magical realms. Rarely, experiments with fundamental forces such as gravity will expose a weakness in reality that allows the Thaumadiastasis to seep into non-magical worlds. Over time, the nature of that universe will change and it will become more magical.
Travel between high-magic worlds seems to be far more common, as magic itself seems to be the only way to allow travel to different seed universes. In many high-magic worlds, wandering into the Thaumatadiastasis can be a real concern. Those beings who manage to find their way into the Thaumatadiastasis often find themselves deposited in a completely new realm if they make it out.