There are at least three layers of existance that are ever-present: The Shadow Layer (The Shadows) The Material Layer (The Worlds) And the Layer of Souls (The Soul-World)
Some describe a fourth layer: The Magical layer
Theories speak of more, but Mages of all Ages and Orders have only been sure of the first few.
The Shadows This is known to be birthplace of the First One and the first four gods to follow him. IT is said that everything exists in the shadows, at all times, and only those that are close to the dreamer (or those that are chosen by him) have access to the shadows. This was proof enough for its existance.
The Worlds The most obvious layer is the layer of physical, material existance. Here life takes place. Here history is written.
The SoulWorld IT took a long time until the Soul was understood. The soul is eternal, and it roams in it's own layer, which is like an abstract mirror of the worlds in its most basic forms. It is said that when a living being dies, the soul, with all the memories that the soul gathered, returns to an untouched place within the soulworld, and remains there until it is ready to live again within the material layer. It is furthermore said that, if a soul is damaged, it can not take part in the material layer without going mad. To damage a soul, though, one must force it out of it's layer or harm it within its layer, and it is only known for incredible magical power to do those things.
Magic Magic is known to have a will of its own, which makes many assume that magic lies within its own layer of existance, just as it is with the souls. As magic is ever-present people either bid or bend the power to their will. During the Age of Magic, magic itself was seen as living power which one could communicate with more or less successfully, depending primarily on one soul's strength. Nowadays it is primarily a tool which one needs practice in handling.
Other Layers There are claims that there are far more other layers. Some say that the heart (emotional feelings) lay on a seperate layer, just as the mind (concious thought) does. So far, though, there is no proof of those layers, nor any other possible layer.