Underdark

The Underdark is a vast network of underground caverns and tunnels underneath the surface of Penastria. It is mostly made up of vast stretches of untamed wilderness, home to a variety of monstrous creatures that are well-adapted to life in these lightless depths. Throughout these caverns one may also find a few settlements, whether they be duergar occupied dwarven holds, deep gnome mining outposts, illithid hive cities or troglodyte encampments. The drow have also constructed subterranean fortresses which protect the tunnels that lie below their homeland of Asshai.

## Geography

The Underdark is divided into three distinct layers, depending on the depth of the layer. These three layers are the Upper Dark, the Middle Dark and the Lower Dark.

**The Upper Dark.** The first 6 kilometres below the surface, this is usually the depth at which one finds the lower reaches of the Dwarven Roads that link the major holds. It is also here where surface dwellers would usually meet with the inhabitants of the Underdark.

**The Middle Dark.** From 6 to 25 kilometres below the surface is usually referred to as the Middle Dark, this layer is where the majority of the known inhabitants of the Underdark dwell, and where most of their settlements can be found.

**The Lower Dark.** Beyond 25 kilometres below the surface is referred to as the Lower Dark, it is unknown just how deep the Lower Dark goes and most of it is unmapped. Even the normal inhabitants of the Underdark know better than to descend into these depths. Those few explorers who have returned from the Lower Dark have described decrepit ruins overrun with crystalline protrusions, fleshy growths, and alien depictions that line its cracked walls. The abandoned halls and tunnels are said to be utterly silent except for the occasional sound of buzzing and crumbling stone.

It's also important to understand that the Underdark is not just a singular cavern, but rather it is divided into different networks of caverns which are spread out throughout Penastria, with that in mind while it may be possible to travel from one network to another, this does not mean that one can always travel from one end of the Underdark to another. These individual networks of caverns are referred to as domains, which function in a manner similar to continents and it's usually within these domains that one finds the largest concentrations of civilisations.

## Environment and Topography

The landscape throughout the Underdark is extremely varied from narrow fissures to subterranean lakes and rivers that conceal caves of beautiful coral, as well as forests of beautifully coloured mushrooms and luminous patches of moss. The landscapes of the Underdark are prone to change due to the effects of tectonic movements, which means that maps tend to be unreliable.

Due to this variation in environments, travelling the Underdark tends to be a far more dangerous prospect when compared to travelling the surface. The lack of light, save for the occasional luminous fungi or moss, means that the darkness is a constant companion. In fact, due to the extreme darkness, there have been mentions of areas where even darkvision does not pierce the veil of darkness. Even torchlight may not always offer the desired reprieve as there are strange flora that seem to draw in light and snuff it out.

Adventurers that delve into the Underdark may also find themselves traversing large swathes of land without any food or water, further accentuating the necessity of preparation especially when one delves into the uncharted sections of the underground. There are also areas where the air has grown stale and poisonous, or it could be explosive due to the underground activity of volcanoes.

## Inhabitants

The Underdark is extremely dangerous and is home to a wide variety of flora and fauna. The animals that inhabit the vast caverns range from chimeric beasts such as Hook Horrors to aberrant monstrosities such as Aboleths which set up lairs in the darkened depths. The plant life that is native to the Underdark is unable to utilize sunlight as a source of energy, therefore much of the flora has evolved into strange and diverse forms in order to adapt to life underground. Some of these adaptations have led to dangerous flora, that have evolved alternate modes of nutrition.