Like all other opposite pairs of houses, the 12th house derives some significations from being opposite the 6th house. The 6th house signifies wellness, the 12th house therefore signifies illness. Related to this is hospitals and hospitalizations; this house is often implicated when someone undergoes surgery, or has been in an accident that has put them in a hospital.
Another 12th house meaning is secret enemies, in contrast to the 6th house signification of open enemies. Truth be told, there is some confusion as to which house is associated with open enemies, the 6th or the 7th. I tend to borrow some house significations from Vedic astrology when I think it makes sense, and here’s one such instance. Traditionally, Western astrologers have attributed open enemies to the 7th house. The reasoning is this: the 7th house is about people with whom we relate closely, so the essence of “keep your friends close, and your enemies closer” places open (known) enemies in the 7th house. On the other hand, in Vedic astrology the 6th house has to do with conflicts and competition, and thus enemies with whom we come face and face. We don’t strive to build close relationships with them, in fact we do exactly the opposite, so the 6th house attribution of enemies makes more sense.
Returning to the 12th house association with illness, when you think of illness as an unraveling of the body, a broader theme of undoing starts to emerge. Traditional astrology says the 12th house is one of self-undoing, of troubles that we bring upon ourselves. Things that were going well start going south. Best laid plans come to nought. With a bit of free association (which itself is a 12th house idea), it is about endings.
Another way to arrive at this notion of endings is to imagine starting at the 1st house of incarnation and the body, then going through all the other houses of various personal and worldly experiences, then finally landing on the 12th, when we are at the end of life. While the end of life might be true literally (illness/age, then hospitalization, then death), more often it is simply the end of a phase of life, whether it be personal or professional, followed by a new cycle that starts at the 1st house. In this sense, retirement is a 12th house signification since it is the end of a career.
Some people might simply live their lives out afterward without engaging in any professional work, but others might take up jobs or creative activities as a necessity or simply to feel alive and valued. The latter are then embarking on another cycle starting with the 1st house, perhaps a “second act”. Frank McCourt won the Pulitzer prize for his bestselling memoir, “Angela’s Ashes”. He wrote the book in 1996, when he was in his sixties, after having retired from a long career as a New York city school teacher.
Continuing to free associate, retirement leads to seclusion, which is also what happens when we are being treated in a hospital (or stuck in quarantine!). But many people choose seclusion. Maybe they are of a retiring (!) nature, who want to be left alone. Or maybe they lead a monastic life, like nuns or ascetics who practice their belief of single-minded devotion to a higher spirit by distancing themselves from social interaction. So convents and ashrams are 12th house places, and by association, spirituality is attributed to the 12th house.
I mentioned earlier that free association is a 12th house thing. Why is that? Pisces is the natural 12th house sign, and Neptune is its ruler, so the significations of both Pisces and Neptune lend themselves to the 12th house. Out of this Pisces-Neptune complex arise imagination, and a sixth sense that travels beyond the material. Free association is an exercise in imagination, letting the mind go where it may, driven by instinct and the subconscious, rather than controlling, rational thought. The is a lack of boundaries with free association is Piscean. This mix of imagination, intuition, and extra-sensory perception makes the 12th house the abode of psychics and clairvoyants. People with Moon in the 12h house, in particular, are particularly tuned to the nether dimension.
Lastly, the 12th house is associated with expense and loss. This can be read in one of two ways in a horoscope. One is that the person is more likely to suffer loss than others, and might have trouble holding on to money because they love to spend. The other is they are especially risk-averse, so they are very careful with their money and do their best to protect their assets. Of course, loss can be about more than just money…
If you have planets in the 12th house in your horoscope, start with the considerations I have laid out in this post to drop anchor, then let your imagination do the rest with some bold free association.