There are plenty of random dungeon generator programs, but D&D 4e presents a pen-and-paper friendly process. Using a d20 and some graph paper, you can construct a full dungeon. However, the mechanics presented in 4e lack details and versatility presented in the random dungeon and random encounters tables in the 3.5 DMG. By combining the two, we can create a useful, elegant, versatile dungeon generator.
This system could be used in any system with a little adaptation. The dungeons could just as easily be a space hulk, the interior of some huge starship, the alleys of a crowded city, or the corridors of a mad scientist's laboratory. All you really need to change is the room descriptions so that they fit your desired setting and feel.
Limiting the Dungeon
Depending on your ruleset, you may want to limit the size of your dungeon. It's pretty common for randomly generated dungeons to run the course of a full character level. For 4th edition, this means 10 encounters. For 3.5, this means about 13 encounters plus change. For pathfinder, this means 13, 20, or 40 encounters depending on the game speed. Once you hit this point, stop generating new parts of the dungeon, and move on to step 3.
Step 1 - Entrance
For some reason, most random dungeon generators skip over the entrance, leaving the crucial question "how do we get in?". The 4e DMG provides two pre-made entrance tiles complete with a staircase leading down into the dungeon, a few decorative touches, and a few doors and corridors to branch off into your new dungeon. Alternatively, you can use a random corridor or chamber from the tables below.
Step 2 - Generate
Start by attaching corridors to each of the exits from your entrance chamber. The heart of the generator is the Corridors table and the Chambers table.
If any of the tables requires you to generate another item (door, corridor, etc.), it will be marked in bold. Corridors are 1 square wide by default.
If you generate a corridor which runs into another corridor, end the new corridor by connecting it to the intersecting corridor. If the corrdiror hits a chamber, either add a new exit to the chamber, or move one of the unused exits to accomodate the corridor.
|1||Straight 4 squares. Continues with another corridor.|
|2||Straight 8 squares. Continues with another corridor.|
|3-5||Ends in door. Continues with another corridor on the other side.|
|6||Straight 4 squares, door on right. Continues with another corridor.|
|7||Straight 4 squares, door on left. Continues with another corridor.|
|8||Straight 4 squares, side corridor on right. Continues with another corridor.|
|9||Straight 4 squares, side corridor on left. Continues with another corridor.|
|10||Three-way intersection ("T"). Roll 1d3 to determine which direction to attach to. Continues with another corridor on each branch.|
|11||Four-way intersection. Continues with another corridor on each branch.|
|12||90-degree turn left. Continues with another corridor.|
|13||90-degree turn right. Continues with another corridor.|
|14-15||Ends in chamber (no door).|
|16||Ends in stairs.|
|17||Straight 4 squares, stairs on right. Continues with another corridor.|
|18||Straight 4 squares, stairs on left. Continues with another corridor.|
|d100||Type (DC to break)|
|01-08||Wooden, simple, unlocked|
|09||Wooden, simple, unlocked and trapped|
|10-23||Wooden, simple, stuck (13)|
|24||Wooden, simple, stuck (13) and trapped|
|25-29||Wooden, simple, locked (15)|
|30||Wooden, simple, locked (15) and trapped|
|31-35||Wooden, good, unlocked|
|36||Wooden, good, unlocked and trapped|
|37-44||Wooden, good, stuck (18)|
|45||Wooden, good, stuck (18) and trapped|
|46-49||Wooden, good, locked (18)|
|50||Wooden, good, locked (18) and trapped|
|51-55||Wooden, strong, unlocked|
|56||Wooden, strong, unlocked and trapped|
|57-64||Wooden, strong, stuck (23)|
|65||Wooden, strong, stuck (23) and trapped|
|66-69||Wooden, strong, locked (25)|
|70||Wooden, strong, locked (25) and trapped|
|72||Stone, unlocked and trapped|
|73-75||Stone, stuck (28)|
|76||Stone, stuck (28) and trapped|
|77-79||Stone, locked (28)|
|80||Stone, locked (28) and trapped|
|82||Iron, unlocked and trapped|
|83-85||Iron, stuck (28)|
|86||Iron, stuck (28) and trapped|
|87-89||Iron, locked (28)|
|90||Iron, locked (28) and trapped|
|91-93||Door slides to one side rather than opening normally. Reroll type (ignoring rolls of 91+). Add +1 to break DC.|
|94-96||Door slides down rather than opening normally. Reroll type (ignoring rolls of 91+). Add +1 to break DC.|
|97-99||Door slides up rather than opening normally. Reroll type (ignoring rolls of 91+). Add +2 to break DC.|
|100||Door magically reinforced. Reroll type (ignoring rolls of 91+). Break DC is 30 for wooden and 40 for stone or iron doors.|
|1-2||Square, 8 x 8 squares|
|3-4||Square, 10 x 10 squares|
|5-6||Rectangle, 6 x 8 squares|
|7-8||Rectangle, 8 x 10 squares|
|9-10||Rectangle, 10 x 16 squares|
|11-12||Octagon, 8 x 8 squares|
|13-14||Octagon, 8 x 12 squares|
|15-16||Octagon, 12 x 12 squares|
|17-18||Irregular, roughly 8 x 10 squares|
|19-20||Irregular, roughly 10 x 16 squares|
|20||One exit plus stairs|
| For each exit other than stairs, roll 1d20: |
1-10, exit is a door
11-20, exit is a corridor
|19-44||Monster and features|
|45||Monster and hidden treasure|
|46||Monster and trap|
|47||Monster, features, and hidden treasure|
|48||Monster, features, and trap|
|49||Monster, hidden treasure, and trap|
|50||Monster, features, hidden treasure, and trap|
|77||Features and hidden treasure|
|78||Features and trap|
|79||Features, hidden treasure, and trap|
|80||Hidden treasure only|
|81||Hidden treasure and trap|
|1-4||1d4 minor features and furnishings|
|4-8||1d4 major features and furnishings|
|9-10||1d4 minor features and furnishings and 1d4 major features and furnishings|
|d100||Minor Feature||Major Feature|
|04||Bale (straw)||Arrow slit (wall)/murder hole (ceiling)|
|07||Bits of fur||Bed|
|21||Cards (playing cards)||Chest|
|22||Chains||Chest of drawers|
|32||Discarded weapons||Dung heap|
|34||Dripping water||Fallen stones|
|41||Flint and tinder||Gong|
|42||Foodstuffs (spoiled)||Hay (pile)|
|57||Mud||Mound of rubble|
|61||Nest (animal)||Partially collapsed ceiling|
|68||Pipe (smoking pipe)||Pool|
|80||Scattered stones||Stall or pen|
|82||Scroll (nonmagical)||Statue (toppled)|
|83||Scroll case (empty)||Steps|
|86||Sound (unexplained)||Sunken area|
|99||Wood (scraps)||Winch and pulley|
|1||Up to dead end|
|2||Down to dead end|
|3-9||Down one floor|
|10-14||Up one floor|
|15-17||Trapdoor plus ladder up one floor|
|18-19||Trapdoor plus ladder down one floor|
|20||Shaft up and down, one floor each way|
Step 3 - Cleanup
These will inevitably be some dead ends, hanging corridors, and other weird odds and ends. Do your best to connect these where it makes sense, or just remove anything which isn't adding to the dungeon. If you have an entire section of the dungeon which is a maze of dead ends, it should either be removed or you should make it make sense. In a cave, crevices in the rock might suddenly end. In a building, sections of the ceiling may have collapsed to block passages.
Step 4 - Encounters
The 4th edition rules have a bit of an advantage for generating random encounters. Because of the specifically denoted "roles" provided in the rules, you can build a diverse, balanced encounter by picking some random monsters with the right roles. By creating a "deck" of monsters, as detailed in the 4e DMG, you can generate all of the random encounters in a dungeon from a small library of level-appropriate monsters.
Most RPGs lack these specific monster roles, so replicating the 4e encounter deck is difficult in most other RPGs. Instead of creating an encounter deck with a grab-bag of monsters and traps, we can get the same sort of feel with a deck of pre-made encounters. These encounters can be any appropriate combination of traps and enemies that provides an appropriate challenge to the party.
Because using monsters of all one power level can be very bland and because it limits our options, I recommend using a sort of bell curve of difficulties. The majority of the encounters should be the appropriate difficulty to provide an average challenge for the party. Roughly 20% of encounters should be difficult, and 20% should be easy. If you want to have a sort of "boss" encounter, add an additional encounter that's exceptionally difficult, and consider reserving it for late in the dungeon.
Random Encounter Types
|3-4||Commander and Troops|
The key component of the Battlefield Control encounter is an enemy with the ability to limit where and how the part can move about the field. Spellcasters and similar monsters make excellent choices for this encounter type. The secondary component is small enemies to take advantage of the party's lost mobility to deal damage.
These encounters feature a single "commander" enemy, either an NPC of higher level than its troops, or a monster like an Aboleth or Mind Flayer which has minions of some sort. The troops typically do most of the fighting, but the commander is the real threat.
A solo monster on its home turf can be a terrifying threat. Pick something big, scary, and self-sufficient. Dragons are a good choice, as are Beholders, and other big, iconic monsters. Alternatively, a single enemy supported by environmental hazards or traps can be a good choice.
These encounters feature one or more melee enemies, and one or more ranged enemies. A party of enemy adventurers can be a great fit in this encounter type.
A pack of weak enemies attempts to overwhelm the party by sheer numbers. Most RPGs have rules for minions/mooks/extras, but if your game doesn't you can still use a cluster of enemies well below the party's power level.