The Dungeon

The Dungeon (also called the Underworld or the Labyrinth) is a vast, planet-wide megastructure of tunnels and chambers that exists beneath the surface of Ersetu. It connects to the surface world through openings both large and small, and descends into unfathomable depths below, creating a habitat full of dangers and wonders beneath our feet.

The Dungeon and Mana

The Dungeon is very rich in ambient mana, and the deeper one goes the higher the concentration of ambient mana becomes. This effect doesn’t appear to ever actually stop. It is rumored that if someone goes deep enough, the levels of ambient mana become high enough to passively induce mana poisoning in human beings.

Ambient mana in the Dungeon flows from some unreachable place deep underground and gradually rises towards the surface, thinning out as it is absorbed by the walls of the tunnels and the life forms that make their home in them. This flow of mana is also usually accompanied by air currents that keep dungeon air from growing too stale.

The Dungeon is connected to the surface in many places. These openings raise the ambient mana levels on the surface by their very presence and are known as Mana Wells. It is widely believed by mages that all ambient mana ultimately originates from the Dungeon.

Ecology and Magical Creatures

The Dungeon is teeming with life. All dungeon creatures are magical in some way, as they rely on the high levels of ambient mana to survive. The deeper one descends, the more powerful and alien the creatures become.

• Surface Layer (Shallow Dungeon): Inhabited by magical creatures clearly based on mundane animals (e.g., fire-breathing beetles, hyper-agile bats). This layer is extensively explored and exploited by humanity. Sections are routinely pacified to serve as storage spaces, dumping grounds, experimental chambers, and mining areas. A number of sapient races make their home here, maintaining complex but surprisingly peaceful trade relationships with humans.
• Middle Layer: Creatures here become increasingly alien and removed from the surface, both in appearance and behavior. Many are unrecognizable by standard classifications. This layer is viewed with great fear by humans, as even experienced mages could easily perish here. Some denizens are sapient but highly territorial, aggressive, and possess an alien understanding of the world.
• Deep Layer: Past a certain point, the monsters become so dangerous that even the best human mages wouldn’t last long. They assume utterly alien forms, challenging common sense with bizarre magical abilities (e.g., existing in two places at once, private pocket dimensions). Fortunately, these creatures are massive mana hogs and cannot survive on the surface.

Origins and Theories

The Dungeon and its place in the world is a mystery. There are multiple theories and myths trying to explain its existence:

• Ikosian Mythology: According to Ikosian myth, the tunnels are the veins of the bound World Dragon. They all converge at the planet's core, known as the Heart of the World, which pumps chaotic vitality and mana into the depths.
• Scientific Doubts: Modern scholars point out the sheer size of the planet and the molten core, which conflicts with the idea of tunnels reaching the very center. Furthermore, scientific models suggest the tunnels should have collapsed by now, indicating an unknown magical mechanism that maintains and repairs the Dungeon.

Regarding the origin of the monsters, there are two main theories:

• Hybrid Theory (Most Popular): Dungeon denizens come from both the surface and the depths. The shallow creatures are surface animals that colonized the Dungeon and developed magic, while the deep, alien creatures originate from the bottom and slowly spread upwards.
• Deep Origin Theory: All creatures originate from the depths. The animal-like ones merely learned to mimic surface creatures to infiltrate the surface.

Economy and Travel

The Dungeon is vital for the modern economy. It is the only source of Crystalized Mana, which powers trains, industrial machinery, and complex spell matrices.

While it is possible to travel through the Dungeon to circumvent surface obstacles, it is highly dangerous. Surface sections are poorly connected, forcing travelers into the deadly Middle Layer. Progress is slow, ambushes are frequent, and dungeon creature flesh is highly magical and toxic to humans, requiring travelers to bring their own food. No one has ever successfully traveled beneath the ocean to another continent through the Dungeon.