The basic building block of a D&D adventure is the encounter. An adventure is really just a series of connected encounters. The encounters themselves can be connected by a map (as in a dungeon), narrative (as in an event-driven game with a flowchart), or by a player actions (as in an adventure using a structure skill challenge).
Slaughterhouse adds an extra layer of design: the zone. In order to understand what a zone is and why it is useful, we must turn to intergalactic bounty hunter Samus Aran. See? I’m going somewhere with that title.
Samus Aran is the star of Nintendo’s Metroid video game series. In Metroid and in other games that are a part of the subgenre that has become known as Metroidvania games (TV Tropes link, click at your own risk), the player explores a single, large, open map. There is generally no single sequence that will get you through the game. Instead, you can explore the map in any order you wish barring certain barriers you can only overcome at specific points during the game. Does this sound familiar?
In order to provide a logical order and sense of structure to the map, it is divided into several thematic regions. The alien planet Zebes in Super Metroid, for instance, is divided into a large jungle region called Brinstar, a series of lava-filled caves called Norfair, and a series of flooded tunnels called Maridia. There are several more regions. The zones themselves are self-contained but also have numerous connections to other zones. Each zone could be thought of as its own miniature dungeon with multiple entrances and exits.
As a side note, there are some other things that Metroidvania style games do extremely well that I am borrowing for my super dungeon and I am sure I will discuss them in more detail later. Right now, the important thing is to understand that you break the map of the game down into a bunch of interconnected blocks.
Slaughterhouse works the same way. The idea is to break your map down into several territories or zones. Each zone should be self-contained, but it should have several entrances and exits leading to other zones. Each zone should also be pretty contiguous in terms of terrain and flavor because the zones become useful tools for placing terrain and hazards.
In my super dungeon, for instance, I might have a zone called “The Sulphurous Pits,” a set of caves near a gate to the Nine Hells. I know that devils wander the region, along with their worshipers and thralls, and I might also create one or two terrain effects (noxious geysers that spout randomly or clouds of hellwasp larva ) that I can place throughout the region.
Your zone map will become an important tool for laying out your adventure. Because each zone has only a limited number of ways in and out, you can map each zone separately and simply make sure the entrances and exits line up. That’s if you are building a dungeon.
On the other hand, your zones map might just be the map. For instance, if you’re using the example of the city that has been overrun by gangs, you aren’t going to map it like a dungeon. Instead, the zones are the districts of the city (and a few key locations) and the players will travel within and between the zones using narrative description or skill challenges. In that case, instead of a big map of the zone, you would probably just prepare a few tactical maps for each zone that you can use as needed (a street in the slums, an alley in the temple district, a market, etc.).
Each zone needs space for four to five to encounters and, because of that, you need twice as many zones as experience levels you plan to cover. This means that each zone is about the right size that it could be covered in one adventuring day. It will probably not always work out that way in play because the party will be wandering from one zone to another. The idea is to make sure that when the party decides to make a dedicate push into a zone (to conquer it), they can do it.
In my super dungeon, I have approximately sixty different zones. In fact, I have so many that I have grouped them together into regions. I had to do that to ensure the party couldn’t easily wander into a zone much higher than their own level. Again, this comes back to some of the other ideas stolen from Metroid involving traffic control and interconnectedness. For a more moderate adventure (one spanning up to five levels), you shouldn’t have to worry over these things too much.
I should also note that in my super dungeon, each of my zones contains room for more than five encounters. Most have room for eight to ten encounters. I did this because I wanted to leave empty areas on the map. For more information on why this is important, check out Greg Bilsland’s recent blog entry “My Dungeon Has Empty Rooms” (check out all of his articles, he’s a smart guy and, unlike me, an actual professional game designer). I also left white space because I wanted the opportunity to move encounters around so that, on a later visit, the party could be surprised when a formerly empty room was suddenly home to a clutch of Acid-Breathing Doom Drakes. Again, that gives the sense of the dungeon being a living place in which creatures wander.
But let’s use a more modest example for the rest of this discussion. I am going to design a Slaughterhouse based on a ruined city that the party will explore. The ancient City of Ur’Gunna Dy was a part of the Empire of Bael Turath. I expect the party to start at level 5 and gain enough experience to reach about level 9.
The first step is to decide on my zones and to lay them out. Well, the first step is to come up with the story hook that brings them to the city and decide whether or not they will have any quests that drive them to do specific things or if they are simply exploring because it is there and filled with treasure and experience. But we’re going to assume I’ve already done that. They are simply trying to reclaim the city.
I begin by coming up with a list of eight zones (because the adventure spans four levels). Most of them will be districts in the city, but there are a few other sites they can explore as well. For example, I come up with The Noble Quarter, The Artisan Quarter, The Market Quarter, and The Slums. There is also an old Fortress, a Palace, an infernal Temple, and Sewers.
I sketch out a quick blocky map of the zones. If I am feeling really saucy, I can even try to make it look more like a city layout. It doesn’t matter.
When it comes time to map the adventure, I decide that the four quarters of the city don’t need dungeon maps. Instead, they are going to involve skill challenges in which the party explores while trying not to draw too much attention to themselves as in Adventure HS1: The Slaying Stone by Logan Bonner (an excellent example of non-linear adventure design with some very fun encounters).