Dungeons. They were originally breeding facilities created by the Demon King to multiply his monster subordinates and increase their individual strength. Afterwards, Ricklent, the genie of time and magic, used his secret magic to turn them into places that humans could use to train and obtain materials.

The basic principle behind their appearance was that when a certain place was corrupted with a certain amount of magic, there was a corresponding probability that a Dungeon would form. Their shape, size and degree of danger varied greatly, and some of the first Dungeons that had appeared over a hundred thousand years ago still hadn’t been discovered yet.

There were Dungeons that only consisted of one floor that couldn’t be distinguished from a normal cave, home to only weak monsters like Goblins, but there were also enormous fortress-like Dungeons with over a hundred floors, crawling with high-rank monsters that even A-class adventurers would have a tough time getting through.

And as the requirement for the formation of a Dungeon was for magical power to contaminate the earth, most Dungeons existed only in Devil’s Nests…

「Is this place a Devil’s Nest?」

『Probably not. If this were a Devil’s Nest, we would be seeing a lot more monsters coming out. This is likely a rare Dungeon that has appeared outside a Devil’s Nest.』

As Darcia said, Dungeons forming in normal forests and fields were rare, but not unheard of. But in such cases, the Dungeons were often not very dangerous.

But if left alone for too long, the monsters multiplying inside the Dungeon would eventually emerge from it and turn the surrounding area into a Devil’s Nest.

There were apparently continents in Lambda whose entire land surface and surrounding oceans had become Devil’s Nests due to this process repeating numerous times.