Yes, the 12th is a house of mystics and mysticism.
The 12th has its origin, in one point of view, in the 4th. It belongs to the "watery" triad of houses -- 4th, 8th, 12th. All three are unfortunate houses, the 4th being less so. All three are dark houses...they are secret, mysterious, unconscious realms. What's in them is "hard to get at", because it's either in the deep unconscious (beyond reach) or within the personal unconscious (which may be accessible under the right conditions).
Mysticism, as I use the word, implies a belief that God (the Mystery) can be accessed directly by an individual, a subjective perception of the divine beyond the ordinary range of human experience. The divinity can't be explained or reasoned because of its paradoxical and unlimited nature; the mystic attempts to experience the divine directly, through what we might call revelation.
The three water houses are the most concerned with this sort of thing. They are the least attached to "the world". And so all three tend to seek "divine union" in one way or another.
The 12th holds things like isolation...the hermit in his cave, the monk in his monastery...self-sacrifice, martyrdom, abnegation, altruistic dedication to the outcasts of the world (the oppressed, the marginalized, etc.).
One of our problems in this world is found in our categorization of things into "good" and "evil". The original sin (in the Bible) involved eating the frut of the tree of the knowedge of good and evil. Seems to me the student should ask "Why is this made the Original Sin?"... Because, on the cosmic scale, there is no good and evil. It's a human invention. Good means "I like it. It somehow profits me". Evil means "It causes me pain and suffering. It brings loss. I don't like it."
And so with this sort of thinking, we find ourselves bound to "good" and "evil", and fail to see that all things carry within them the seed of their opposite. So we say the 12th House is "evil." And it is if all we are looking at and for is our immediate comfort and happiness.
But it the house is Bondange (prison, handicap, addiction, insanity), then it also must be LIberation. But to become liberated, we must first be enslaved. All houses, planets, signs (astrological symbols....and in truth all things in the universe) have both a positive and constructive aspect intimately connected with a negative, destructive aspect. Shiva, god of destruction, is also the god of creation. All things manifest on a "sliding scale" (an axis with two poles) of "good" and "evil"; the two are not separate.
In overcoming our blindness to this unversal fact -- the bipolar nature of good and evil -- lies the secret to liberation. A mystery fit for the 12th House.
If Venus and Mars are in Leo, and in the 12th, and especially if the cusp of the house is held in that same sign....
Then might it not be that false or unearned pride might be a self-defeating power in the life? And the answer to that might be found in the exercise of magnanimity, of open-handed generosity, of letting one's personal light shine disinterestedly (ouch) for the good of all...and other sorts of Leonine positive manifestations.
The Sun disposes Leo and the planets and houses contained within the sign. So Sun is the first place to look in understanding this configuration in your chart. What is his condition, what does he "say" in your chart? In most cases, you will discover "underlying causes" and "final outcome" in the dispositor of house and planets. Look up the word in your dictionary..."dispose", "disposition", and "determine", "incline", "order"...in order to understand the function of a dispositor. Rulership is of first importance.
Astrology is an art founded upon analogy. Only when you have trained your mind to think in terms of analogy will astrology open itself to your understanding.
Mars is red. So he symbolizes, by analogy, all things that are characteristically red: blood, rust, anger ("seeing red") and all passions (which are "red hot")..............and then, the more direct and obvious analogies carry even more analogies within them.
Fire is ruled by Mars. Oxygen is necessary to combustion. Mars rules oxygen. Blood comes forth from cutting and piercing. All sharp edges and points are ruled by Mars, and things characterized by them, such as swords and needles.
Both Venus and Mars are directly and personally -- and inherently -- concerned with different aspects of sexuality. Mars, who rules penetration, is lord of the phallus and of the aggressive, outwardly active passions. Both are in your 12th house. (Gandhi had a conjunction of these two in Scorpio there -- in the chart I use, which is not the commonly accepted one), and he fought with "lust" all his life. Twelfth House difficulties can often be overcome by sublimation. Gandhi finally tamed his lust through the practice of Brahmacharya, and then had access to that immense power of lust directed toward purposes other than sex.