Travel in the Underdark
The vast, lightless Underdark is a dangerous place indeed. To native beings, its darkness and tight confines can be insurmountable terrors. To Underdark natives, lights mean danger - either they are lures to bring travelers to some predator or they mark the place of creatures too powerful to fear attracting attention to themselves.
Much of the Underdark was created by volcanism, flowing or dripping water, earth tremors, and mysterious magic that left behind an intense magical radiation that the drow call faerzress. Any of these forces can cause sudden collapses, floods, or falling hazards.
Drinkable water is all too rare, apt to be guarded by predators or already in use by molds or fungi dangerous to other creatures. Some waters are acidic, corroding metal, flesh, or both. Bad air is another problem. Both the native cities and the ongoing volcanism can generate poisonous vapors that drift or creep for miles in the lightless depths.
The Underdark is not a static, unchanging place. Drow, deep gnomes, and other races that dwell in subterranean cities claim the prime territory. Purple worms, umber hulks, xorn, and other creatures burrow through solid rock. Fell races such as beholders and illithids wield strange spells and powers to shape the rocks around them, while the dwarves simply tunnel with skill and determination. Mysterious, unexplained appearances of chambers, caverns, and passages that pulse with strong faerzress are not unknown. Underdark maps thus soon go out of date. Guides can be helpful but their loyalty is always a matter of concern.
Travel or teleport magic is usually useless over long distances in the Underdark because it is warped into deadly failure by faerzress, though it can still prove useful for short journeys within the same open cavern. Portals work in some areas but not in others, and the establishment of new portals is well nigh impossible, since the magic involved attracts formidable enemies very swiftly. Like the established trade routes, known portals-are always guarded or closely watched.
Supplies are another problem. Only in Underdark cities are shops to be found, and those cities are widely seen as collections of murderers and thieves.
The very lack of supplies in the Underdark has created vigorous, ongoing trade. A merchants' caravan may provide the best protection to a visitor to the Underdark. The large amount of carried supplies and fearsome fighting capability, magical and mundane, of a caravan offers safety in unsafe territory. However, care must be taken to avoid unintentionally offering oneself as a slave while employing such a tactic.