The best way I know of doing that is through meditation. In meditation, you turn your attention inward, away from the forms and phenomena. Yes, of course, this world is a product of the mind's imagination. But it is possible to transcend the mind. The mind does not have an independent reality beyond the consciousness which gives rise to it, in the same way that the wave is not separate from the ocean. That pure ocean of consciousness is all that there is. As I say though, you need to have a direct experience of it. Without that, it is just a concept of the mind.
Apparently the only way to know it is to experience it.