The mental realm of existence is where perception of both time and space begin to break down. Traditionally this is associated with the energy center in the head. The subtle body associated with mental energy is normally the one most people use to project their consciousness out of their body.
Most systems operate by feeding, or transforming, vital energy into astral energy and then into mental energy. If performed exclusively without sufficient effort, and nutrition, to reinforce the body frequently this results in a slow kind of wasting of the physical body. The phenomena is most often witnessed in the broken down appearance of lifelong monks and religious people. They literally sacrifice the physical for the mental.
Mental energy proper exists as a kind of timeless and spaceless, as in lacking spatial parameters, force.
Generation occurs by taking the astral energy described in the last post and drawing it into the head.
Once again, hold the breath at the end of the inhalation, except this time the energy expands outwards. Subsequently on each movement of the breath, both inhale and exhale, the sensation expands outwards from the very center of the head to a sphere about three feet in diameter surrounding the head.
Very strong practitioners can expand this to fill rooms. I’ve been told, but never personally witnessed, that the strongest can fill an area approximately 25 meters in diameter.
Most people travel outside their body using the mental body associated with their physical form. Generally speaking this is safe and the body enters a kind of sleep state.
Using this method the practitioner can visit anywhere in the near earth and astral realms. Frequently this devolves into a kind of astral tourism. Fun, but largely a waste of time.
Travel within the pure mental realms is rather confusing.
These are the lands of concepts such as true morality and the meaning of the color blue. All of this has value depending upon your personal goals, but expressing what goes on in physical words is frequently difficult. Meaningful to the individual to be sure, just hard to apply in the land of the here and now.
Since these places lack concrete spatial dimensions the actual sensation of travel is rather relative as well. The good point is that this is where duality ceases and as such negative entities largely do not dwell here. Not all concepts existing here are healthy, or of any value whatsoever, to an incarnate human either, but they are not technically malicious.
Many groups spend most of their time mucking about the upper astral and the mental planes as these are relatively easy to get to in comparison to physically manifesting phenomena or going into the truly enlightened realms. Likewise, both of these regions are still governed by the laws of karma. However, engaging these planes, and their inhabitants, requires the least amount of transformation on the part of the individual practitioner. They also represent vast expanses and contain a fair amount of interesting, if not useful, information.
In short, you can spend several lifetimes screwing around here without needing to advance into the great beyond.