Sanctum of the Makers
The Underdark is a vast subterranean network of interconnected caverns and tunnels, stretching beneath Kalrythia and forming a literal underworld, where many hostile creatures roam. It is a strange, alien setting, entirely underground. Bizarre creatures and ancient races populate it, nearly all of whom are of hostile nature. Many of these creatures, suck as Rock Worms, helped form then Underdark as we know it.
The Underdark is extremely dangerous, especially to creatures that are not native to it. There are the usual dangers associated with caverns: claustrophobia, occasional poor air circulation, and getting lost. Cave floor and ceiling collapses are also a hazard.
There is no light except for occasional patches of phosphorescent fungus; most Underdark inhabitants either have highly developed senses other than sight or have developed Darkvision. Food can be extremely difficult to find, and much of the natural vegetation is poisonous. In addition, potable water is seldom easy to locate in this setting. The Underdark is permeated with a magical energy the Drow call faerzress, which is used as a source of energy by the native plant life but which interferes with scrying and teleportation spells.
There is no unified underground government, although there are individual city-states, each with varying forms of rule. Thus there are cities ruled by an autocracy, magocracy, matriarchy, monarchy, theocracy, and so forth. The underdark economy primarily deals in armour, exotic goods, magic, slavery, timber and weapons. The ethical code of many indigenous races tends toward evil or indifferent behaviours; good natured sentiments are rare.