Dungeons.
They were places that existed in a separate space from reality, usually connected to it by some sort of doorway.
They were created in one of two ways, either naturally through a concentration of large amounts of mana in a single location over a long period of time.
When left unabsorbed or undisturbed, that mana would eventually distort space itself, creating a separate domain that usually reflected its nature, in other words, a dungeon.
And finally, powerful individuals, who often those who stood at the peak of the world, would carve out a space beyond reality and leave behind trials, knowledge, or inheritances.... mostly because they were bored.
This dungeon was a result of said boredom.
"A dungeon?" Renelle repeated as she looked at the massive doors before them.
"Mmh," Adrian nodded, "a dungeon created by the headmistress's father."
"What's inside?" She asked again turning to him.
"I have no idea," he truthfully answered.
