I just finished reading The Omega Point by Whitley Strieber. Central to the plot is a painting which serves as an interdimensional portal: People can walk through the painting into another world.
Immediately after finishing this novel, I began reading an entirely different book, Sane Occultism by Dion Fortune. On p. 15, I found this:
The grandeur of [occult] theories ennobles human life and enables us to see our fate and acts in a perspective related to the cosmos; but is that glorious background interstellar space or painted canvas?
There is only one test, to walk straight up to it and see whether the stones of the Path are beneath one’s feet or if one has simply torn one’s way into the sordid back premises of a theatre.