Underdark Basics

The Underdark is an enormously wide-spread network of natural and constructed tunnels that run under the lands of the Forgotten Realms.  These tunnels and caverns are typically five to 20 miles below the surface, and have very few connections to either the deepest of those shallow diggings known as "dungeons," or with the surface of the Realms.  Our adventures will start out in the Underdark regions between Waterdeep and Anauroch, in the "savage north."

The Underdark is home to many horrid or fascinating creatures; most of these races of monsters and humanoids are ancient, dating from before any humanoids walked on the surface of Toril.

The most notorious race of Underdark humanoids are the Dark Elves.  They are vicious
and cunning enemies.  They live in huge underground cities run by their nobility and led by the
priestesses of Lloth, the Spider Queen.

For centuries, Dwarves and Dark Elves ("the Drow") have waged war beneath the Forgotten Realms.  The dwarven halls are in decline, now, and several of their kingdoms are completely gone, their strongholds abandoned or taken over by hostile humanoids.

Other races making their homes in the Underdark include:
 

Underdark  Economy

 The Underdark produces many goods that are marketable there and on the surface world.

 Likewise, there are items that can only be imported into the Underdark:

These products are typically brought to the Underdark by trading companies run by surface-dwellers.  Many trading companies have hidden and well-defended warehouses near connections to the surface.  Acquiring and trading goods here can be a profitable business for someone with the courage and skill to survive in the savage depths of the Underdark.

Technical Notes about Adventuring in the Underdark

Darkvision is the extraordinary ability to see with no light source at all, out to a range specified for the creature.
Darkvision is black and white only (colors cannot be discerned). It does not allow characters to see anything that they could not see. otherwise-invisible objects are still invisible, and illusions are still visible as what they seem to be. Likewise, darkvision subjects a creature to gaze attacks normally.
The presence of light does not spoil darkvision. If a character has darkvision with a 6o-foot range, and he stands within a 2a-foot radius of light, the character can see normally in the light, and 40 feet beyond the light because of his darkvision.

What you can and can't do with darkvision:  Most of the Underdark races have superior darkvision, which allows them to see in the lightless depths.  There are limits to what can be accomplished with dark vision, however.

In general, beings with darkvision CAN:

In general, beings with darkvision CANNOT:

Movement Rates:  Traveling through the Underdark is much more akin to dungeon-crawling than moving overland on the surface.  However, most of the main tunnels of the Underdark are clear of  debris, are fairly level, and are big enough for travelers to move a little more quickly than when carefully exploring dungeons.  The movement rate in typical Underdark tunnels is the character's movement rate in miles per day (a "day" being a 10-hour period of travel in each 24 hours).  A party of characters moves at the rate of the slowest character -- a dwarf or gnome in the party can slow the movement rate to 6 miles per day!  However, a dwarf (including duergar and derro) or gnome (including svirfneblin) can perform a "double-time" march to double his movement rate.  At the end of a "double-time" march, the dwarf or gnome must make a DC of 15 (dwarf with no penalty, gnome at +2 on DC check) example would be make a DC check of 15 to keep running while being chased and the gnome now has to roll 15+2 because of the penalty which is 17; a failure indicates that for the remainder of the day (the next 14 hours), the dwarf or gnome is weakened and fights at -2 to hit and damage, a +4 to all ST DC (plus penalties for DC checks are bad) and CN DC checks, as well as suffering a -2 penalty to initiative (initiative negatives for check are bad also because you want to roll high, highest initiative always goes first).

Day and Night, Calendar:  The Underdark is a realm of eternal night.  As such, it is very difficult for its inhabitants to follow the typical calendars of the surface world.  As trade with the surface is so vital to most Underdark cultures, however, most cities of drow, dwarves, svirfnebli, duergar, and derro attempt to at least be aware of the passage of time in terms of surface calendars.

In the drow city of Menzoberranzan, for instance, time is kept via a huge stone pillar called Narbondel.  At the start of each "day," a drow wizard casts a fiery spell into the base of this hollow pillar; throughout the day, the fire rises, heating the pillar and making it a bright beacon to those with dark vision.  Then as the day progresses, the fire subsides, eventually fading into darkness.  At that moment, 24 hours have passed and the wizard returns to re-cast the fiery spell for the next day.  Not only does this system keep the drow aware of the passage of time on the surface, but it also makes it possible for citizens of Menzoberranzan to agree on meeting times.  Narbondel's Peak (noon) and the Black Death of Narbondel (midnight) are typical choices.

For those living away from civilization, however, accurate timekeeping is extremely challenging, if not impossible.  Underdark travelers are frequently surprised when they reach a city and find that they've miscalculated the passage of time by days or even weeks.

Air Supplies:  Breathing in the Underdark usually isn't a problem -- unless you're around a wizard who loves to cast fire spells.  Large fiery magic will quickly deplete oxygen in a small cavern, and worse, the smoke has nowhere to go! It typically takes 2-8 turns for an area to clear out once filled with smoke, and the smell can linger for months at a time afterwards.