Contemplation
You can discard most of the junk that clutters your mind (understanding that these things really only exist there - in your mind) and clear out space for yourself by:
contemplating the scale of the world
contemplating infinite time
thinking of the speed with which things change - each part of every thing; the narrow space between our birth and death; the infinite time before; the equally unbounded time that follows.
— Excerpted from Marcus Aurelius Meditations: Book 9, Meditation 32
photograph by Lisa Thrower