Realism, idealism, materialism, naturalism, phenomenalism and all such are practical mythologies for rendering the extraordinary telescoping nature of experience coherent, or as coherent as may be. You could say that the underlying stuff of all things, their substance, is consciousness if only consciousness were anything more that an idea, or a character in these myths, but what you mean to point out is that all you can see is seeing and all you can hear is hearing and all you can feel or think is feeling or thinking. The question turns on its head once you pull out the pin, and the pin is the reality you surreptitiously endow on the image that represents you in whichever of those myths is currently in play. It's no problem that there should be such an image, it's there for you, but it belongs to the myth, is made out of nothing but the believing.