Mysticism seems to be largely misunderstood.
It seems to be either thought of as a kind of dark, ethereal and vague mystery that can never be really known, or as an impractical and vain lofty exercise that can never truly be achieved, at least in this life.
For me, it is neither.
In my own experience, it is nothing less than coming directly face-to-face with the most radical Realism that can be known by the human mind, the utterly naked face of Reality as it is, stripped bare of all adornment, category, thought, judgment, ego, self, consideration, game, or question.
It is bare bones Truth. It is what absolutely and ultimately Exists and Is—nothing more, nothing less.
It is the courage to face the Truth with all the blinding force of a million suns without squinting. It is knowing things as they really are, with all the reality that Reality is. Reality. Reality. Reality.
There is nothing misty, shady, or “mystical” about it.
It is knowing Truth so deeply that you realize you are one with it, that it is you, that you are it, and not some spiritual or supernatural truth, but the most real Truth there ever was and ever will be. It is Truth as it is.
It reveals the most Natural Eternal Law and Universal Order that exists, and this saturates everything, and you are part of it. You exist because of it. You are a manifestation of it, a reflection of it, an unfolding of it, and you are in it.
You come to realize what you are, the most fundamental, real, essential, bedrock of your Being and Existence. You see it. You know it.

…”mystical” experiences, as we dubiously call them, are not nebulous, vague or maudlin—they only become so when we debase them by verbalization… In fact, its primary mark is the sensation that this state is more real than any other one has experienced before—that for the first time the veil has fallen and one is in touch with “real reality,” the hidden order of things, the X-ray texture of the world, normally obscured by layers of irrelevancy.
(Arthur Koestler, The Invisible Writing (New York: Macmillan, 1954), 350-353.)