Gaze into the darkness of your closed eyes as though it were the sky, totally unobstructed. And see if you can feel that there's no boundary here. There's no indication of the size of the scope of awareness. There's no edge to your visual field. There's no boundary that defines the energy of your body. There is simply what appears. And everything is appearing in a condition that is totally undefined.
This is, again, an instruction to visualise, or feel ("see if you can feel") the boundarylessness or limitlessness of the inner space as the ground for all arising mental events.
Since this is so central to Mahamudra / Dzogchen meditation practice, and to the concept of realisation in that tradition, I quote again Daniel P Brown on this point.
I do this with two quotes: the first is from an introduction to one of this translation of so far secret Bon texts. The second is from a live retreat, where the theoretical text has been transformed into pointing out instructions.
Here, Daniel P Brown notes that the full experience of limitlessness is a part of the "enlightenment" process.
Pointing out limitlessness serves as the basis for the realisation of enlightenment. In order to fully experience limitlessness, it is important to see if the ordinary mind has imposed any mental constructions of edges or boundaries upon limitless space . If so, the practitioner "opens" (...) his or her awareness directly into any edges or boundaries, like pouring space into space, until the edges dissolve like mist into the atmosphere. The practitioner continues this process until all residual impositions of edges and boundaries disappear and there is a direct experience of genuinely limitless empty awareness/space (Daniel P Brown in intro to Gyaltsen et al., 2022, p 117)
This theoretical statement is turned into pointing out instructions in the following passage to perform a "moving into" operation:
Now investigate if this field of knowing awareness-space extends in every direction, like an infinite vast expanse. Boundless. If the ordinary mind imposes any edges and boundaries on this awareness, you can move right into the boundaries and edges with your awareness. When you move into the boundaries with your awareness, they immediately dissolve like mist dissolving into the atmosphere. Keep moving into all the edges and boundaries. It is like pouring space into space, pouring awareness into awareness. If the ordinary mind imposes edges and boundaries somewhere further out, just keep moving into those edges and boundaries with your awareness, until it is perfectly clear to you that this awareness is boundless, edgeless. This field of knowing awareness space is timeless and changeless on one hand, and boundless, edgeless on the other hand, like a vast ocean of changeless, boundless awareness (Pointing Out the Great Way)
Gyaltsen, S. T., Gurung, G. S., & Brown, D. P. (2022). Self-Arising Three-fold Embodiment of Enlightenment: [of Bon Dzogchen Meditation] (English Edition) (2nd ed.). Mustang Bon Foundation. https://www.amazon.com/Self-Arising-Three-fold-Embodiment-Enlightenment-Meditation/dp/195695001X