Dungeons are places that hold great fortunes, but at the risk of exceptional danger. They're usually inhabited by Monsters, which serves to guard the treasures. In the world of Re:Monster there are several scattered all over the continent, and many more can be found at various Labyrinth Cities, like Purgatory and Aquarium. Through some unknown method, Monsters and Bosses slain in certain Dungeons will re-spawn.
There also seem to be ranks for Dungeons, from lowest to highest being ranked such as :
The Demigod, God and Great God rank Dungeons are grouped as Age of the Gods Dungeons. It is said that there are only five Great God Ranked Dungeons in the world, and that within those places, powerful beasts like Dragons come in large numbers, rather than as bosses. By conquering the dungeons of this level, one could gain a portion of divine power