Deep below the Surface
It's best to keep some things buried and forgotten, there's a reason why people hid them underground. Even we have secrets we don't like to share.
Below the surface of Fabulae lies a whole new world named the Subterrane. Being a world of caves and underground realms, not many people know of its existence besides maybe a few Dwarves who dug too deep.
Although civilisations have risen from the darkness of this area, life down here is considered harsh and sometimes unbearable. Whether it be from the constant conflict for survival or the ecosystem evolved to live here, no native will consider the Subterrane a safe place.
An Underground WarzoneEveryone who has grown up in the darkness of the Subterrane knows how dangerous it can't be: miles long cave systems, scarcity of food and the sole fact that everything has adapted to live in the shadows. The settlements that hold vast are strongholds against any threats, with any civilisation living within them being sceptical against anyone from outside the walls. It's no surprise that the many races that dwell here are in a constant fight against one another, whether it be enslaving others to act as personal armies or laying waste to local
The Layers of the Subterrane
Upper LayersThe upper layers sometimes touch the surface world, mainly in the forms of large open holes in the crust or even giant caverns just peaking into the regular grounds. Giant forests and underground ecosystems are common, with some even being known to the surface world. The civilisations that rule here are mostly Dwarves and Drow, with the latter taking up the most residence here. Wars typically tend to break out here solely out of the sheer fact that resources can be scarce, as the Drow Empire especially likes to try and claim ownership of the whole layer.
Middle LayersThe middle layers is where the Subterrane goes from looking a bit like the surface world to being actual caves. By now you will find more abnormal creatures and wildlife live down here, almost alien ecosystems of fungal and insect being common. Some downright call it alien. Here, societies typically consist of Duergar and even Trox, who build the equivalent of fortified bunkers here. Cities are difficult to get in or out, being more akin to glorified mazes than actual settlements.
The Depths are as deep as people can go without either dying of heatstroke from being so close to the core or being burned alive by magma. Most of it isn't even accessible without directly mining into the caves or using teleportation spells to reach it.
Creatures that do live here have adapted to the extreme heat, whereas civilisations are so sparse that only ruins are found. Some of the other depth-dwelling races don't even know who built these cities, believing they were swallowed by the crust millennia ago and lost to history.
The Depths of Fabulae