Mr. Buhlman's book is very much in keeping with the ideas about the nature of the nonphysical dimensions as experienced by Robert Monroe in Journeys Out of the Body and related by the near death experiencers in Raymond Moody's Life After Life and many others. The picture drawn by all of these is of an after-life that is really a continuation of this life, but at a higher level (or "frequency") in a universe that is multidimensional.
In essence, our physical world is a low and dense environment that we, as spiritual beings, express ourselves in through physical bodies (flesh-and-blood). We do this, as the consensus among writers on this subject seems to be, in order to grow and develop as sentient beings. The hard knocks of this physical life promotes that growth. As Mr. Buhlman says:
Each of us is currently experiencing the most effective system of growth ever devised: evolution by direct personal experience, by the very act of being.
Mr. Buhlman says that the ability to separate your spiritual (higher energy) self from your physical self (i.e., leave your body) is inherent in everyone and a very natural and safe thing to do. He provides instruction on how to do it in the last part of his book. This instruction consists of techniques (relaxation and visualization techniques) that can lead to a conscious separation from the body and experience of higher frequency environments (sometimes called the spiritual or numinous worlds). He says that daily practice of these techniques usually results in a person being able to attain a successful out-of-body experience (OBE) within thirty days.
Once a person is able to separate from their physical body, Mr. Buhlman suggests they engage in active exploration. In agreement with Robert Monroe, he says the first environment a person will find is the close, energetic one that is a near duplicate of the physical:
...the first nonphysical dimension is a parallel energy world almost identical to the physical universe. This dimension of energy existing close to the physical world is molded by the consensus thoughts of the six billion inhabitants existing in the physical.
We even have an energy body that seems to be especially designated for expression in this near-physical dimension. It is often called the "etheric" body and Mr. Monroe spends more time on it than Mr. Buhlman. But both recommend separating from this second body in order to explore the higher dimensions ("moving inward" is Mr. Buhlman's term for this further separation, and he describes it as a fast, moving, or traveling sensation).
Mr. Buhlman also talks a lot about is the malleability of the higher frequency environments to sentient thought. That is, when you're there, you think about something (like a park or a house) and it's there. You think about going someplace specific, and you go there (walking or flying as you imagine). There are even long-lasting environments created by the consensual imaginings of many beings (heaven and hell? Vahalla? Disneyworld?). This lends some credence to the premise of The Secret and suggests that there is some power to the idea of positive thinking. It also suggests that the Golden Rule is a really good basis for personal morality (because it keeps thoughts positive if actively practiced).
I've read many books on out-of-body experiences (OBE), near-death experiences (NDE), communications with the dead, and such over the years so I'm used to such mystical concepts. Readers with a similar background will not freak at Adventures Beyond the Body and will, I believe, find it enjoyable and enlightening. I found its biggest value to be its expansion on concepts that Robert Monroe introduced (like techniques for achieving an OBE) and his positive, nonspooky attitude in talking about all this. For readers new to this subject matter, I would recommend keeping an open mind and reading without judgment. If you don't dismiss it right off, it will take a while to digest.