The Book of Formation sports an impressive exercise with 231 gates: Imagine the physical world as a murky, black ground. In your mind, engrave into the earth the twenty-two Hebrew letters. They shall form a circle around you. Carve the letters out from the ground and erect them, to form a circular wall of letters. Finally, imagine lines ascending from the letters passing in a half circle over you to the opposite letter, creating a dome above and around you.