After you have focused on the breath, moving in and out of your nostrils. You start to focus on seeing the black of your closed eyelids. Now look, not through your eyeballs, and see without seeing the space that isn’t spatial, which seems to be behind your eyebrows and inside your frontal lobe.
Your conditioned mind will try to assign it a color, and you watch this take place physically as the “space” turns into all sorts of colors and shapes, until you are finally able to let go of your need of seeing a physical thing and it undresses from its colorful and shapeful cloak.
You are no longer looking at something else that seems to have a contained space inside your frontal lobe but instead it opens up and spreads in all directions so that immediately you are with it and in it and there is no distinction between you and this “space” that is everything and nothing and you’ve lost all memory of sitting there on your cushion and just balance up and out of it, until a door slams shut or a bright light flashes or something else brings you back to the physical world in your seated body.