Dungeons

Dungeons (迷宮 （ダンジョン）, Danjon, Labyrinth) are mysterious buildings that appeared fourteen years prior to the current storyline. It is commonly known that, if one clears a dungeon, he or she will be bestowed with riches and power. They are ruled by Djinn. Magi have the ability to make Dungeons appear and disappear at will.

History
After the desolation of Alma Torran, the surviving populace remained in underground cities for five years until they exhausted the remaining resources and moved to the new world created by Ugo. Solomon's 72 Household Members who became Djinns stayed in the underground cities  while the cities themselves becomes dungeons. There, the Djinns wait for the King Candidate for them to choose. Fourteen years prior to the start of the series, a strange building rose from the ocean. This was the first dungeon, Baal. Scientists and soldiers alike took an immediate interest in it and, before long, there were a plethora of researchers who came to investigate the strange phenomenon. Their curiosity soon led them to explore the dungeon. However, none from thousands who entered left with their lives, which caused people to refer to it as "the hole of death". As people began to give hope on learning of the secrets of the Baal, one exploration, headed by Drakon of the Parthevia Empire was successful in their endeavor. Sinbad, a boy recruited by Drakon to help conquer Baal, was bestowed with the powers of the Djinn within it, Baal.

It is later revealed that the first Dungeon was summoned by the Magi, Yunan.

Description
Each dungeon is different in appearance and difficulty. All have a different interior and exterior. This is because the Djinns that rule each choose the appearance or difficulty as they see fit.

Entry to Dungeons
All Dungeons have only one entry -- through a gate. The gate is generally a semicircle and radiates a golden light. Upon entry, the feeling is similar to that of a mucous membrane.

Upon entering the Labyrinth's gate, one will fly through a pillar of light. Upon advancing on the correct path, treasures await. It is here that the Djinn Container can be found.

Trivia

 * Despite the fact that the world has only known about dungeons for the last fourteen years, the first known instance of a dungeon appearing is over 200 years ago by Scheherazade when she had her first King Vessel.
 * Ugo has explained that Dungeon Entrances are portals to Alma Torran, where the Dungeons are located.