The underearth-the region of caverns and realms beneath even the deepest of dungeons-is teeming with life. Many cultures have been there for as long as life has existed in the sunny reaches above. Other races have been driven there by violent conflict with kindred races of the surface. Where do these races live? How do they interact with each other and with outsiders? What do they have to offer a group of adventurers from the surface? Creatures such as the drow, duergar, kuo-toa, and myconids are revealed in their natural environments-environments virtually unknown to even the most experienced adventurers from the surface. The histories of these fabled races are also treated briefly, as a reference for the Dungeon Master. Many adventures can be drawn from these histories, providing a wealth of conflicts and challenges for many gaming sessions to come. There are also detailed random location and encounter generators, allowing for exciting adventuring with little or no preparation time.
The DM receives a great deal of attention when running underground campaigns. There are many intricacies of the underground campaign, and Dungeon Masters are always open to suggestions for designing adventures to challenge (and perhaps throw a scare into) players. Maintaining a strong, highly motivating story element is an important part of a DM’s job. Suggested conflicts, always the first step in a powerful story. The ultimate random element of any game is the players. How do you handle players who always try to do the exact opposite of what you want? What if your campaign has gotten out of hand because of too much treasure or powerful magic in the hands of the PCs before they’re ready to handle it? Must such a campaign be discontinued, or are there ways to salvage it?
The fantasy role-playing game systems already provides rules for a great number of player actions, ranging from combat and movement to barter and negotiation. Many situations arise, however, that have not been addressed by the rules until now. Can a character who is not a thief climb a rough stone wall? What if a PC, thief or not, has to fight a creature and cling to the wall at the same time? Or combat an opponent atop a swaying footbridge? Can your heavily laden character possibly jump that yawning chasm? All these unusual situations, and many more, are covered by rules, else the Dungeon Master can make it up as you play, as long as the DM’s ruling is consistent. How much use is a mule in a dungeon? And what about that river? Is it possible to swim underwater to avoid the monstrous sentries on the bank? Those shiny stones over there-are they worth anything? An assortment of rules to make the underground reaches as wide open for adventuring as the forest or meadow that surrounds your characters’ home village.