The astral plane has long been regarded as a dimension that sits next to, or on top of, our physical dimension, which can be accessed via our spirit form according to many different religions.
Interestingly enough, it seems that the CIA had put in some time and effort in regards to accessing the astral plane, among other things, as detailed in a released document on their website.
The 29 page document has diagrams, methods and other fascinating pieces of information regarding the subject.
Worth a read.
