Three different grounds I am noticing in immediate awareness right now...
The first is the Ground of seeing and seen, absent of any I anywhere (not fully awakened to itself, but clearly noticeable.) Awakening to Ground seems centered in the head.
The second is the ground of fertile darkness, the ground of form. Awakening to the fertile darkness, the black loamy soil allowing any form to emerge from it, seems centered in the belly.
The third is the ground of bliss, a ground of experience. This seems to be the ground or nature of any experience when it is allowed to be as it is. When it is free from the drama of trying to hold onto it or pushing away. When the center of gravity shifts out of the particulars of the experience and into the seeing of it or the Ground. Awakening to the ground of bliss seems centered in the heart, it is a quiet joy of simply experiencing - independent of what is experienced. (A heart awakening brings of course far more than just that.)
The Ground of seeing and seen is the Ground of the two other ones, although there is certainly a sense of emptiness, void and pure potentiality in the fertile darkness. The ground of bliss is clearly within the seen, within form, within what comes and goes.
And as with anything else here, this is completely provisional, completely open for revision (and revolution), and coming from very limited experience. It is just how it appears right now.