In a lightless cavern deep under the surface, tenebreans dwell. They live where no one can find them, far from the rest of the world, in marvelous cities that no one has ever seen. They have no respect for gravity and little for physics in general. Their cities defy possibility and imagination, using every esoteric art at their disposal. Without vision, they have no need of obeying any aesthetic rules outside of something tactile or auditory. They build for echoes. Every city is malleable, changed by the whims of those who live there.

The leaders of any tenebrean city are called atereans. The atereans are responsible for mediating conflicts, coordinating tasks for the community, and leading defense if they are ever attacked, though in the history of their civilization, they never have been.

Children are raised by the whole community. They are taught from a young age how to shape the metal and stone around them and to use various esoteric arts. When they are ready, they can choose to study only one specific art or skill, or they can take up multiple arts, which is more common. By the time they have enough skill, they are adults and can become independent. They usually continue study for a long time after. They usually have mastered at least one esoteric art before midlife.

Gender is complex and fluid among them, and courtship rituals involve use of esoteric arts to show one's love and affection. Marriage is unknown, but there are some commitment ceremonies. Relationships are fluid as well, however.

The use of shadow most, and they use it well. It is the center of their culture. They exist in the dark, and therefore, they are one with it. They use shadow in art, in entertainment, and in competitions. They keep no accounting of time, but every so often they gather to celebrate, compete, and share their arts. The use of other esoteric arts to supplement this is not uncommon, but the most revered are purely shadow.