So here we got – part two of The Underdark is online, in case you missed the first one:
Not too long ago I had one a discussion on player perception and your hardest job (at least for us in our gaming group) is to deliver the same perception of the situation to everyone, no matter if (s)he played for years and is a dungeon master himself or if (s)he played only for a few hours and actually does not care a lot about rules, story and the lot. This if course is true for UNDERDARK adventures, your job as a dungeon master will be to create an environment for your players to call home, for the time of their stay. But this “home” will be a lot different from what most of us are used to, that mentioned I hope most avoid having various mushrooms growing in their homes ;).
The environment
Hardly two forest look alike and that’s the same for the underdark. You will have to come up with a few ideas on your own and there will be distinctive differences to various regions down below. Still a basic question you might want to consider: What can survive underground without light? Fungus, worms, earth-elemental and related creatures and plants, everything related to negative energy (undead) will not have a lot of problems either, as well as shadow-related stuff, after all there’s shadows everywhere down there.  And of course magical creatures, demons and the like, who can survive in some of the most unpleasant areas without problems. Regarding light, this will be hardly encountered in these places, there might be mere shades of colors every now and then when you’re encountering phosphorescent shrooms, but this will be hardly enough for the human eye. Furthermore it’s useful to give the players a few hints, for example in the real world it’s most often the case that particularly shiny animals are poisonous, maybe in your underdark those have a specific (or terrific) smell on them.
Suggested plants
Plants are important, even underground, they define the surrounding area and add a lot of FLUFF to your game. Previously mentioned phosphorescent funghi are a great start, secondly think about screamers, again these are funghi which happen to emit a painfully loud noise when someone accidentally touches them. Those are great plants to secure and underground environment and are hard to forget for your players since they leave a distinct memory of someone standing next to them when you’re sneaking towards a secured site. Thomas (one of our dungeon masters) has made a nice, brief introduction to edible plants in one of our latest sessions, which was very enjoyable, he described distinctive features of a few plants underground and told everyone howto prepare them in case we are running low on food – while not particularly something everyone will remember for every plant described, you might want to pick a few tasty descriptions and describe those things to your players as well… For this I suggest you think about – roots, stone-like plants and funghi – perhaps add a moss or two.
General conditions
Humid or wet someplace over here, dry and hard to breathe at other times… The air is one of the most important features of your descriptions, you should focus on these details every now and then to give everyone a good idea of what they are up against. Furthermore smooth stonework or rough stonework are considerably different (and most important closer to civilisation) than giant wormholes that are insecure and look like they come crumbling down on you any time… Add a few features of wooden bars here and there, don’t forget a little bit of vegetation, maybe ants, termites or “their underground cousins” *evil grin*. (Did I mention in the first post, everything is a little more nasty when you’re underground?). Caverns and (especially stoneworked) hallways can carry sounds a far distance, give a thought to echoes and bizarre, distorted noises once in a while and you got a good idea of how it might feel in the guts of your players. A marching small troop of warriors might sound like a harbinger of doom, on the other hand, it will give everyone a good idea of how important it is to actually be silent and not walk screaming aloud while underground. Finally add a few hard-to-define gadgets for your players if they tend to be curious. It should be a great playing-ground for alchemists and the like, leftovers from breeding places, stripped-off (snake)skins and remains of bones should not be missed, strange-smelling secretions and slimy mud is something that gives a riddle to many a player. (Our gnome ended up at a monster-pile larger than himself standing on his toes last time… and felt like – not so nice an area when he saw it…)
Encounters
Keep in mind that not every encounter in the underdark is lethal for your party. Even though you have a lot of predators lurking, not everyone is dumb enough to jump the next best target without actual study. Sometimes it’s easier to kill a rothé or lizard than going for a heavily armed adventurer, more than a few creatures in natural underground environment realize that. In general encounters will be tougher than above ground but it’s more important than ever to have a concept behind every encounter. A scout patrol is probably easiest to imagine and random encounters are possible, but a handful of undead below ground will most often be tied to a special location or person. A scout patrol not returning from their errand will be nothing special, but two or three of them disappearing in the same region might catch the interest of more powerful individuals. Drow, duergar, illithids and the like will probably not fight to their death, they will either try to retreat or diplomatically approach or trick the players. Especially lone survivors of previous clashes might give the characters. The main key here is – a good preparation of experience and some skills at improvisation. If you’re running a d20 adventure, you might want to have a look at some official material over at Wizards.
Great follow-up! Good points on making the Underdark a sandbox.
Questing GMs last blog post.. – RPG As An Academic Subject
Excellent!! Good Article