Very good book - Touching Enlightenment: Finding Realization in the Body by Reginald A. Ray Ph.D. (Author)

The book describes anatta and losing boundaries into total exertion/Maha (cosmic body) expressed in another way through the portal of a body. The practice is similar to Vipassana or Satipatthana.

https://www.amazon.com/Touching-Enlightenment-Finding-Realization-Body/dp/1622033531/ref=sr_1_1?ie=UTF8&qid=1480434415&sr=8-1&keywords=touching+enlightenment
 
“Through his own deep experience, Reggie Ray skillfully guides us into an awakened bodily life. He offers necessary, wise, and liberating practices of realization within our mysterious human form.”
Jack Kornfield, PhD, author of A Path with Heart
Touching Enlightenment provides readers with a fresh look at the steps required to turn our understanding of enlightenment into full embodiment—a vital process that determines the way in which we actually conduct our lives. An indispensible book for the serious practitioner.”
John Daido Loori, abbot of Zen Mountain Monastery and author of True Dharma Eye: Master Dogen’s Three Hundred Koans
"Reggie Ray’s approach to the dharma is wonderfully fresh while also radically rooted in the foundation of the Buddha’s meditation instruction—mindfulness of body. He has a richly textured understanding of the lived body as the vessel of wisdom mind, as well as the carrier of all the karmic patterns that obscure this pristine awareness. Highly recommended."
John Welwood, author of Toward a Psychology of Awakening 
Excerpts:

"This breathing practice also helps us uncover the energy that ultimately is the big toe... ...our seemingly solid physical sensations of the big toe are a substantialized and solidified experience of a more primary experience of the big toe: that it is actually a vibrating, scintillating field of energy... in a sense, we become the energy of the big toe, we are it."

"... by sensing it and feeling it, not just as the body does, but as the body. We begin to experience moments when we realize that, fundamentally, "we" are the body. As we find ourselves in greater and greater somatic embodiment, we discover deeper and deeper contact with this world. At this point, our conclusions about it recede into relative unimportance. Life is then less and less about thinking and more and more about simply being."

"When we bring our breath consciously into different parts of our body, there is the physical part, in this case pulling the breath in through the pores of the skin. But at a deeper level, there is the inner breath, by which we are bringing the life energy into that particular part of our body..."
"...Now you are breathing through the entire body, through every pore of the entire body, into every portion of its interior, all its bones, muscles, and organs, into all the cells of the body. Just work on that for a few minutes. It isn't easy, but if you stay with it, the energy, attention, and sense of intense vitality will become greater and greater.

As you are breathing through the entire body, notice if there are any places that perhaps seem a little dead or a little resistant to the breath, and you can emphasize those areas a bit. You are still breathing through the entire body, but you are ending up in that particular spot, trying to bring more life to it, more energy, more awareness, more feeling of being awake and sensitive and sentient.

Continue this for another minute or two. Try to make a lot of effort now, maximize your effort and exertion to the utmost, breathing in through every pore of your body, into every single cell of your body, surface and depth, simultaneously.

Then when you think you can't possibly do any more, you can just let go of the technique and lie quietly. Feel the energy circulating throughout your body. This is the inner breath, the prana, which is your vitality, flowing through your nadis, or energy pathways. Your body is now very, very awake, and you can feel an electricity flowing everywhere. Stay with this for several minutes, enjoying it and being completely in the flow. Stay with it until you feel really satisfied. After resting for a few more minutes, you can sit back up. As you do so, continue this sense of the full body, cellular breathing but gently now with a very light touch."

"We realize that our body feels, senses, knows its interconnection with all things. In fact, we are, we exist, only in and through interconnection; ultimately, we are nothing other than "interbeing," in Thich Nhat Hanh's beautiful phrase. All of this becomes increasingly clear the deeper we enter into our somatic existence... ...modern science is showing us that there is no solid, impermeable, discrete envelope to our individual body and that we are in constant and open-ended exchange with our larger bodies, just as our brain is with our lungs, our bones with our circulatory system: the same principle, just a larger scale."

"We have seen how the interior of our physical body unfolds first as more open than we had suspected, then as the space of our own awareness itself. In our further unfolding, again we saw, we discover that this "interior space" is not limited to our body at all, but is to be found "outside" of us, as a cosmic reality, in the earth beneath us; in this unfolding of our cosmic body, we discover an increasing boundlessness to our own awareness."

"...This standpoint, so to speak, of an experience of the earth beyond subject and object opens the way for the unfolding of a different way of being in and with the rest of the cosmos. Initially, we may begin to feel something very strong calling us - calling, calling continually: a mountain we have seen, a glacier, a particular valley, an open vista, a certain hillside or place in the forest, a tree, a river, a lake. We start to sense - although we cannot quite believe it - that the mountain, for example, is alive, and aware, and strongly inviting us, pulling us in its direction. There is something about it that is drawing us to it in the most compelling way. We may dream about it at night and feel its call during the day. What we feel is entirely somatic: our hearts are on fire and its call is resonating throughout our bodies. Such is the depth of somatic life, of *feeling* life, that is now becoming our way of being."

"Have you ever been present to a raindrop falling on a window sill, watched its great globule tumbling into sight, splashing on the sill, spreading out in slow motion, and exploding into a thousand specs of light? Have you ever gazed into a campfire, suddenly finding yourself within it, discovering your own state of being as nothing other than the raging inferno, burning, burning, burning, fueled by all it meets? Have you contemplated a lake and suddenly found yourself lost in its endlessly wet and watery world? Have you glanced up into a great tree only to meet an ancient presence looking back at you with immense understanding and care? Have you ever, one day, looked up at the sky and realized with a sudden, electric shock that courses through your body, that you are meeting a vast shimmering awareness, incredibly alive, that is watching you, utterly seeing you through and through, holding you within its boundless love?"

"...The mountain is our heart, the running streams, our blood; our mind, the limitless sky; our thoughts, the small passing clouds. Ultimately, we are nothing other than these."

- Touching Enlightenment
A video that Thusness and I found to be very good.

https://www.youtube.com/watch?v=0xc3XdOiGGI&feature=share
Last year, Thusness wrote in a discussion with a follower of early Buddhism who doesn't identify with Theravada,

"The key issue about authenticity is centered on the idea of whether authenticity is based on the 'words of Buddha' or the 'teaching of Buddha'. All the four tenet systems have claimed their authenticity and each generation based on their experience, studies and realizations attempt to integrate these four tenets. If (authenticity is) strictly based on the 'words of the Buddha' then Mahayana isn't by definition Buddhism, of course.

...Yes Nixon, Vajrayana has their culture incorporated into Buddhism. But when we talk about Mahayana teaching, I think the cultural aspect has to be put aside. Rather, we should look at Mahayana as a development based on the 'teaching'. It is a development over time about what exactly is the right understanding of the 'teaching'.

...Many are linked to political systems and which sect is in power and their 'closeness' to the ruler, so we also cannot assume popularity as authentic either.

...We have stripped out those magical elements and fantasies when talking about the teachings as well. Many are simply metaphorical. Great teachings often blend themselves into cultures and teachers often used their cultural background settings as a base to explain and make people understand the deeper 'meaning' of certain ideas. Now, we must also understand that 'logic' is not the only way of understanding. Some insights are triggered not with rational induction or deduction theory. So a development of a great teaching to allow someone to understand something deep requires us to have multifaceted discipline and instrument.

We are not just a rational being. We dream and fantasize.. to understand our nature, our suffering, our way of understanding, we got to know ourselves too. When attempting to know what Buddhism has developed into a particular trend, these are all needed. However for deciding whether what is authentic, these are not needed."

Thusness then discussed the Tathagatagarbha teachings:

"Tathagatagarbha is a potentiality, the idea that everyone has the capacity to actualize oneself to Buddhahood. Invented as part of a reaction towards the strong movement of Hindu culture. Hinduism is basically based on Brahman and Atman - the eternal Self, and Buddhism's anatta is a direct contradiction against that. It is for this reason that Mahayana developed. In all the four tenets, the middle way, the yogacara, the sutra school and Vaibhashika, all are based on the fundamental understand of the three universal characteristics.

That said, in every system, there is surely some of those hiccups that deviate from the definitive view. Even in Theravada, we see the Thai Forest traditions promoting Poo Roo - The One Who Knows, as ultimate. Many foreigners in the West that are less informed can mistaken that to represent the teaching of the Buddha too. There are those who go even further to say that Anatta implies 'not self' as the five aggregates are 'not self' and the essence of the teaching of anatta is to find the True Self, quoting instead the Kevatta Sutta on the luminous mind and consciousness without features.

Buddha Nature is thus not a problem peculiar to Mahayana, in all traditions we see this.

To me, I'm a non-sectarian, so I am quite free not having prejudice for/against Theravada, Mahayana or Vajrayana. We get our experience and teaching to release, as well as to relief ourselves from our suffering from a great teaching.

To come to our understanding of what is the fundamental cause of our suffering, and the core teaching of Selflessness is not that straight forward. We experiment and test our paradigm to see if it works. It is a life experience and journey.

In my experience and journey, there is essential two paths. First is taking and seeking comfort in the ultimate and carrying it throughout, and the other, is looking into the fundamental core of suffering and understanding its nature. So there are basically these two - one relies on the essentialist practice that they need to have an ultimate, and the other says no... there is no need to, you just have to understand the nature of suffering. Therefore when we clearly see this, we realize that Buddhism is based on the latter, and the whole development of Theravada and Mahayana is based on such a system. Otherwise there is no difference from other (religions). As such it depends on an individual path and which core system one believes in.

For me, the essence view has in a certain sense proven to not be the way and I greatly appreciate the Buddha's path. To state otherwise would mean that Buddhism is using the view of an essence to solve suffering, which isn't true for me."

"I just appreciate Buddhism as a beautiful teaching and Buddha as my teacher, as a student doing something for a teacher... nothing more than that. I seldom participate in discussion as I am not a scholar and cannot contribute much."

"It's not in my nature to seek Buddhism. I have a strong Taoist background and passion for Hinduism when I was young. So philosophically and culturally, essencelessness is not a view that suits me. But it takes painful experiences to come to a willingness to let go, to see the truth of impermanence and anatta. To challenge and come to an understanding that you don't actually have to do this and that.... (or have an) ultimate here and there to release. But rather to truly accept and look deeply into impermanence, then you will let go and we can come to a new understanding of the relationship of suffering and the truth of suffering having to do with a fundamental paradigm we hold so dearly.

..Your mindset and experience can change, so is your understanding, and you just begin a new path with new understanding. Impermanence from personal, micro and macro view. You see when you see impermanence and use it as a door in practice, your view changes also, from Vipassana observing the minutest sensations in our bodily sensations to appreciating a view in current quantum physics, macro view, to observe events. So our idea changes and we adopt such understanding in our life over time. Sometimes it really depends and it needs the right condition and situation to trigger it, just like the case of financial crisis."


...

[24/3/19, 11:17:05 PM] John Tan: From the perspective of clarity, it is true that Buddhism anatta and emptiness is more profound and deep… lol. But still good to caution about respecting all religions and practice. Why empty clarity is only pointed out in buddhism. So although it is true about all points to pure consciousness, it is realizing the emptiness that is the prajna eye to allow us to clearly see the empty nature of clarity. Otherwise we will most likely land in alaya or [be] required to still in deep stillness of samadhi.”