Catacomb

"The Catacomb is something unexplainable, a force of nature that humanity doesn't yet fully understand. Like the discovery of black holes, it changed the way we perceive and understand the universe. Imagine an Earth made up of layers instead of being spherical. The seven continents don't lie on a globe, but on seven different layers connected via unique passages. To move from, say, layer five to layer six, you would need to find one of the numerous passages spread throughout that link the two. This is essentially what the Catacomb is, a world of layers, and the gates on Shole Island somehow act as portals that lead directly to the top layer of the Catacomb, what we call the First Floor. But it doesn't end there. The Catacomb extends downwards into infinity, or at least, it appears to, for humanity has yet to reach the Bottom Floor. And the further one descends into its depth, the more dangerous but also more wondrous and fantastical it gets. For literally anything can happen in the Catacomb; it is a place where magic is a reality, where monsters and myths roam, where adventure lies around every corner, and where humans can attain the power of Gods. And as, over time, humans began to realize this, the Catacomb increasingly became a destination for people all around the world. For people like me." - Shepherd, Chapter 1