The Labyrinth
Also known as the Dungeon, the Abyss, the Hells, the Depths and many more names throughout history and folklore. The Labyrinth is a never-ending expanse of tunnels, underground networks and more that seem to fill the world's crust. It is said that within the deepest reaches of the Labyrinth, The Daemon still rests within something known as the Obsidian Tomb, sealed away thousands of years ago by the might of the Faedra and The Celestial after the death of Nature's aspect.
The Labyrinth itself holds possibly hundreds of "Floors". Though this is a term used lightly to describe one rough level within its depths, a single floor may not be precisely even by any means and go up or down depending on the internal layout. However the shift to lower levels is usually fairly clear as they are often spiraling tunnels, sheer dropoffs into the darkness, or ancient staircases within some ruins.
These are Firstborn ruins that are found within the Labyrinth itself, generally in the upper layers but by no means only such. Especially as the discovery of many Daevata that have been found within the lower levels. The source of these ruins are believed by scholars to stem from the twilight years of the Firstborn's era, where they began to panic at the realization of their own impending extinction. As the sun's rays grew too strong, the other races too plentiful, and the loss of their slave race the Humans they retreated underground. Here they slowly evolved into the feared Daevata through corruption. Some even making deals with The Daemon to survive.
Due to this, these great ruins are full of ancient Firstborn technology and magic, granting access to rare relics and mystical items beyond what most mages can ever hope to accomplish. These ruins have been reported down as many as over fifty “floors” within the corrupted depths. As such many adventurers, scholars and researchers tend to enter the depths in search for these ruins to acquire knowledge, mystical lore, artifacts, and more.
Due to the Corruption of the Labyrinth itself, corrupted species are rampant within the depths, and as such it is feared as a "realm of monsters". Though food grows within it, the corruption has caused it to be deadly for most to eat and as such bringing rations and water is paramount to the survival of most explorers. The deeper one delves into the depths, the more one is faced with what many common folk call "Demons". Though their true species is known as the Daevata or other corrupted species such as The Pale whom are feared by most for their ruthless raids on the surface to acquire brood-mothers and food.