Q. What is our Second Mind perceiving? Plato says we are only viewing shadows on the cave wall, not reality.
A. "Reality" depends on the viewing mind. From the First Mind view, the reality experienced is that of external things (objects) as well as internal subtleties like thoughts, feelings, desires. On close inquiry, however, objects begin to break down - they become particles, then fields, then even subtler. This is an indication that the world of things we see is a perceptual interpretation, not what is fundamentally present. This is what is referred to as 'shadows' by Plato.
From the Second Mind view, what is seen is the light behind the shadow and how it plays to project the perceptual world, including this body, mind, and the feeling of internality and externality. We can say it is the deeper reality. Beyond this is the Third Mind, pure potential.
So reality is defined in accordance with the perceiving mind. Recognizing this, the mind is free to experience the vast tapestry of life, far beyond the common stories our society generally limits itself to.