The 12th house relates to that which is hidden from view. Ruled by Pisces, spiritual practices like meditation, shamanic vision quests, past life regression, dream therapy, psychic development, and hypnotherapy fit into the twelfth house.
This is the place you go for your privacy. It also shows what you would like to hide from the world, but will need to deal with at some time in your life.
For example, Mercury in the 12th house is often the child who is told that he/she talks too much, so learns to be seen and not heard. However, as the child gets older, they must learn to communicate all over again.
The 12th house is where we want to escape from the world, and this can include alcoholism, drug addiction, or any time a person lives excessively in their fantasy world. In the 12th house, you need to look at the shadows of your inner being in order to bring forth your connection to the One Source of all that is. This energy can be used positively through contemplative spiritual practice or other forms of self-analysis.
Photography, the ocean, and secret societies are associated with the 12th house, as are prisons, hospitals, and psychiatric facilities.