The megadungeon is the most famous part of Dungeons & Dragons and it’s successors.
Sadly, there aren’t that many, as they can be difficult to put together and key and come up with original layouts for level after level after level.
I’m going to throw my hat in the ring and put out a tool that I think will help make this job easier and fit the theme and tone of your campaign.
Dungeon – Wilderness synthesis is the term I have come upon to describe this system of adventure design. The dungeon does not exist in a vacuum. For the purposes of this game aid the Dungeon will be considered a living, if not precisely sentient, component of the Campaign Setting.
The Dungeon is not only living, but instinctively aware of intrusion by creatures or beings from the world above. It is wholly inimical to such intruders and will take steps, through the inhabitants or through the construction of traps and mazes, to dispose of them. (For more on this approach, see Dungeon as Mythic Underworld by Philotemy)
To begin with, the Dungeon comprises all of the underground levels, however many there may be, right on up to the surface of the earth above. The various creatures that may be encountered on the land above the Dungeon will have their lairs below, in simple or complex arrangements.
Determine the Wilderness Encounters and Lairs
Draft a one-mile hex at the appropriate location in your setting. Use a piece of hex paper and draw an outline of this one-mile hex composed of nine hexes across, flat side-to-flat side.
There are 90 “200 yard” subhexes within the one mile hex. The center hex of this larger, one-mile hex, is where the Main Entrance to the Dungeon is located. Roll a d20 to determine what kind of structure or place contains the Main Entrance.
D20 roll Structure
1-3 Shrine (uninhabited)
4-5 Tower (possibly inhabited)
6-7 Keep (possibly inhabited)
8-9 Temple Complex (possibly inhabited)
10 Single Tomb
11 Ancient obelisk in front of a massive door
12-14 Castle (see p 182, DMG)
15-16 Ruins (roll d10)
1-3 Ruined Tower (possibly inhabited)
4-6 Ruined Keep (possibly inhabited)
7-8 Ruined temple (possibly inhabited)
10 Ruined Castle (possibly inhabited)
Use the appropriate wilderness encounter table for the terrain your megadungeon is located in to roll for whether or not the structure is inhabited, and by whom. If a certain result doesn’t make sense, roll again, or choose. In the case of a Temple, you may wish to include the followers of a god that fits a particular niche within the adventure you are planning.
Wilderness Lairs and Encounters
There will be X monster lairs that exit onto the surface of the earth above the Dungeon, where X = the number of levels you plan to generate (up to 9). There are 90 200-yard hexes in the large, one-mile hex.
- Roll Xd90 (use an online dice roller!) to determine which 200-yard hex each lair entrance is located.
- Roll XdX to determine the Dungeon Level of the nine monsters that make their lairs in the dungeon. Assign each result to a location on the appropriate level.
- For each location, roll on the appropriate Random Monster Table for the assigned Dungeon Level, making a note about which monster is assigned to which Dungeon Level.
- Look up each monster in the Monster Manual, then roll to determine the Number Appearing. This may be a very large number, in the case of some humanoid monsters. This indicates the lair is home to an entire tribe, clan or what have you.
- For a monster which has a “Number Appearing” value of up to 25% of the maximum, assign the lair to one level higher (level three rather than level four). This monster may be encountered on the assigned level, the next level above or below, and on the ground level.
- For monsters with a “Number Appearing” value 26% to 50% of the maximum, assign the lair to the original level. This monster may be encountered on the assigned level, the next level above and/or below, and on the ground level.
- For monsters with a “Number Appearing” value 51% to 75% of the maximum, assign the lair to two levels lower. This monster may be encountered on the assigned level, the next two levels above and below, and on the ground level.
- For monsters with a “Number Appearing” value 76% to 100% of the maximum, assign the lair to four levels lower. This monster will be encountered on the assigned level, the next four levels above and two levels below, and on the ground level.
- Monsters encountered above or below the level of their lair will be 5-20% of the total Number Appearing, acting as a Patrol.
- Any result indicating Undead imply the existence of an animating Necromancer. The Necromancer will be a Level Five Cleric (or equivalent) with the Animate Dead spell. The original undead creatures will be encountered on the assigned level, additional Skeletons and Zombies will be encountered one level above and below. The Necromancer may be encountered on any Dungeon Level.
Create Wandering Monster Tables
The assignments above will allow you to create a Wandering Monster table for each level. This will be a 2d12 table, with 11 entries. The tables will likely be fairly similar, using choices from the appropriate dungeon level tables from the DMG.
The 2 result will be the highest-level monster with a lair on that level (as determined above), the 12 will be the highest-level monster without a lair on that level (again, from the list of nine monsters determined previously). The 7 result will be the lowest level or most common creature on that level, including creatures like Rats, Giant Insects, Slimes/Oozes or another “signature” Common creature for the particular level.
Each level or group of levels should have a theme, or at least a specific atmosphere. The results of 4, 5, 9, and 10 should be encounters that reinforce that theme/atmosphere.
Next week we will create a sample of the process, generate all 9 Surface monsters, their lairs, and one Random Table for a Lair level.
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