Even the world of appearances, filled with physical bodies, is a concept of the mind. Colors, qualities and forms are concepts. All are concepts of the mind. Nothing can be known outside the mind. The uninhibited mind conceives of all that exists.
Existence appears like a wave on the Ocean.
Enlightenment is the state of mind that transcends all dualities, and finds the freedom in it. Call it anything you like, it is still one thing. There is nothing else. The One Mind rests upon nothing, and has no source. There is nothing else to realize.