The Planes

The planes of exsistence are infintely large dimensions seperated physically from our own. They are connected on a magical level and can be accessed thus. Each plane has a semi-stable core that powerful mortals such as the Sliver of Divinity may visit through magical or divine means. These cores range from a few miles to several thousand wide and tall. Outside the cores are wastelands that vary depending on the planes structure.
For example the elemental plane of water. At it's core is the islands and vast deep oceans teeming with intelligent life, powerful creatures of the deep, and civilization at sea. The further your travel from this core the deeper the oceans, the less common the islands, and the more feral the waves and beasts within. This general rule applies to all of the planes. None have ever found a limit or source for these planes. Few could survive exploring them.

The Planes Wheel

The most popular interpretation of the planes is the wheel. Organized into the four morals, lawful, evil, chaotic, and good. The top of the wheel is good, the bottom evil. The left represents order, and the right chaos. The planes seem to reflect the unique combinations of these four traits. The inner four planes are the elemental planes that pour into the positive and negative planes. Those six together form to make the material world as we know it.