My current Pathfinder campaign (the “Elania Campaign”) looks to be heading into the Underdark.
For those who may not know, the “underdark” is a specific part of the Pathfinder “world” that includes a variety of races and monsters that live underground with their own ecology, economy and politics. Perhaps the most well-known of underdark denizens are the “Drow” or the “fallen elves.” Drow elves are presented as the descendent of elves whose pursuit of power led them to practicing the “darker arts” of magic, which ultimately led them to avoid the light of day and move underground.
But there’s a lot more to the Underdark.
In my own world the Underdark is probably more similar to the “official” world of the game system than any other part. The Drow do live there, and there is an entire underground system of caves, tunnels, caverns and domiciles where entire nations live their lives with the world above taking little notice unless something from below decides to make some noise on the surface.
Having said that, the main concern I have about the Underdark portion of my campaign is that I have virtually no terrain built for that purpose. Most of my terrain is either outdoor terrain or else are buildings of some sort.
The one thing I do have is dungeon terrain, which will at least give me an entry into the Underdark. Eventually though the worked stone of dungeon walls will have to give way to raw earth, caverns, or things carved directly into the rock itself.
So… seems like I’ve got some work ahead of me…