Hedin is an underground net of kingdoms.
After the Battle of Gratown against savage mongols of Ertagerak, the people of Artinon was massacred. A man and her wife fled to the mountains, but they were followed by the flesh-eaters Gertagons, a wizard-like group of monsters, pets of the mongols of Ertagerak. The only hope was to hide into a cave (gertagons hate dark places). Inthere, the family found a place where some sunlight was able to enter, and they decided to remain there until the retreat of the Gertagons. They lived eating some berries that had grown thanks to the sunlight. After a year, the wife bore three children. But the place where they had been born had a mysterious effect on the children, such that they enjoyed to live into the dark caves, crying everytime the parents tried to take them out of the caves. After many years, it was a numerous family, and the siblings began to marry themselves. It is the main cause of the really low genetic diversity of the hedans. Some couples left that cave and they discovered a complete net of underground interconnected caves. They founded many underground cities, and they sowed more berries in near-to-surface places. They also began to eat roots from the plants and many underground beasts. After one thousand years, they remain unknown for the most people of Earth.
It includes over 400 kingdoms hidden beneath. The kingdoms are communicated thanks to a underground net of caves, and they are distributed through all the world.
They are just normal humans. To compensate the lack of solar light they have to eat food with abundant vitamins.
Each city has a hundreds of torches to illuminate the city. Those torches are lighted up using the fire of the Hearth of the Royal Palace. This Hearth is sacred for hediners, and the first daughter of the king is devoted to the preservation of this fire. Roots of old trees are used as wood for the fires.
Needing of oxygen
The Oxygen proportion of those caves is stable, as strong breezes hit the mountains that hide the caves, introducing large mounts of fresh air into the deepest caves. However, the 1700's El Bebe Northern Oscillation changed the climate in a devastating way, change the direction of the breezes thus choking many kingdoms of Hedin.
The man and her wife who founded Hedin were transformed into gods by the myths of Hedin. The man was named Hedinon, god of wisdom, represented as a boy with a crown, and her wife was transformed into Nirad, goddess of life, represented as girl with a torch. Local cities also deified their founders, and the hediners are very devoted to their gods, building temples and appointing priests.
Deepest kingdoms are dedicated to the mining, while superior kingdoms does agriculture of underground berries.