Dungeons in the world of Death March kara Hajimaru Isekai Kyusoukyoku. The demon lord mostly appears in labyrinths or the outskirts around them. According to Arisa, there are 6 living labyrinths on the continent Shiga Kingdom is located (Seryuu City labyrinth was not counted). Besides the Seryuu City labyrinth, the last labyrinth appeared 100 years ago. It is written in books that labyrinths appear where the corpse of the demon lord is.
Labyrinths grows by giving birth to monsters and sucking up the life of adventurers who come seeking for magic cores. As a labyrinth deepens, the monsters in it gets stronger. It sucks up magic power from its surroundings and refines it into magic cores.
According to Arisa, there was once a labyrinth which the dragon encamped. It's known that there are no labyrinths encamped by dragons right now.WN 4-8