Hollow Earth is a subterranean world below the surface of the planet Earth, inhabited by both humans and Abnormals. It consisted of an enormous cave network that crisscrossed the Earth's crust and in some placed penetrated the mantle layer.
The city of Praxis is located there, and its guardians patrol the surrounding area. There are multiple gateways to Hollow Earth that can only be opened by a keystone. All the entrances to Hollow Earh are equipped with sensors and vampire detectors, and if they detect vampire blood, then a laser field activates which forces the intruders down the vast network of granite tunnels to the nearest Praxian Garrison. The tunnels within Hollow Earth are well lit due to many pillars that outline the cave systems.
There are many vicious abnormals within Hollow Earth, many of whom are extinct on the surface, including the Basilisk. Humans and abnormals not only live in the city but also in the outlands where they live in nomadic cultures or outland tribes and move to seasonal camps to farm large mushrooms called Rashi. All beings within Hollow Earth are ruled by Praxis, often with an iron fist, although it has been noted that Praxis's harsh laws are the only thing keeping Hollow Earth's dangerous abnormals from overrunning the entire planet. The rock surrounding the city contains a high percentage of lodestone and magnetite which helps with their communications but also acts as a natural electromagentic shield, but the supply tunnels a few miles above the city are primarily granite in composition. The only way to enter Praxis is by airship or by one of the outland gates.