The Aethyrs are a metaphysical system of personal development that exist outside of physical reality. To use this system of development you must be in some form of altered consciousness. In altered consciousness we mean, meditation, out-of-body travel, mental travel, or even conscious (lucid) dream travel. You can and do travel to these realms in an unconscious dream state; however, your conscious self does not benefit from such an encounter. With conscious manipulation of your inner-self into this nonphysical development system, you are accelerating your evolution by a magnitude of 10,000 to 1.
The Aethyr system is not an easy one for self development, though it is a quick and precise one. In using the system you must be ready to expose and bring to the surface all that you dislike in yourself. Each Aethyr level is designed to expose any flaw you may have so that you can see it and know that it exists within you. Then, it is up to you to work on removing that flaw from your personality. The many deities that you will meet in and through the Aethyrs are glad to help you as long as you are ready to help yourself. They will give you the guidance, protection, knowledge, and energy to conquer any personal-development obstacle that may stand in your way. The wondrous part is that these beings ask nothing in return for their services except that you be sincere.
There are 30 separate Aethyrs (reality planes) each seemingly stacked one on top of the other broken down into seven major divisions. The lowest of these planes is the physical plane but the actual Aethyrs begin just above the Physical Plane on the Etheric Plane. The highest of these planes is the doorway out of human existence as you know it.
Some of these sections are separated by a ring-pass-not. These ring-pass-nots are barriers that must be passed before you can move on to the next major division. For example, to reach the Etheric Plane and the Aethyrs residing there, you must be able to leave your physical body behind and travel with your spirit and consciousness to that level. The physical/etheric ring-pass-not prevents you from taking your physical body with you.
The idea is to visit each Aethyr, preferably in order, from bottom to top (though this ordering does not always need to be adhered to strictly) and experience the lesson that each Aethyr has to offer. Most of these experiences are quite pleasant, as long as you don't push yourself too fast or too hard or grow impatient and attempt a lesson you are not yet ready for. The Aethyrs possess an alluring quality to them that gently nudge you upward in development. As soon as you master the lesson in one, you quickly gravitate to the next level.
The accompanying guide is designed to help you with what to expect and not expect on each particular level. Remember that your experiences will be personal to you and may differ slightly or greatly from what we have outlined here. For example, a castle to some people could be a space station to others, a knight could just as easily be a cowboy. The lesson is what is important and how that lesson gets delivered to you will depend on who you are and what you like or dislike.
* additional source material: "Enochian Magick" by Gerald J. Schueler, "The Golden Dawn" by Israel Regardie