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Random Dungeons

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.

Corridors

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.

Random Corridors
d20 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.
19 Dead End.
20 Random Encounter

Doors

Random Doors
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
71 Stone, unlocked
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
81 Iron, unlocked
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.

Chambers

Chamber Size and Shape
d20 Chamber
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
Chamber Exits
d20 Exits
1-5 None
6-11 One
12-15 Two
16-17 Three
18 Four
19 Stairs Only
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
Random Chamber Contents
d100 Chamber Contents
01-18 Monster only
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
51-76 Features only
77 Features and hidden treasure
78 Features and trap
79 Features, hidden treasure, and trap
80 Hidden treasure only
81 Hidden treasure and trap
82 Trap only
83-100 Nothing
Random Features
10 Chamber Features
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
Random Features and Furnishings
d100 Minor Feature Major Feature
01 Anvil Alcove
02 Ash Altar
03 Backpack Arch
04 Bale (straw) Arrow slit (wall)/murder hole (ceiling)
05 Bellows Balcony
06 Belt Barrel
07 Bits of fur Bed
08 Blanket Bench
09 Bloodstain Bookcase
10 Bones (humanoid) Brazier
11 Bones (nonhumanoid) Cage
12 Books Cauldron
13 Boots Carpet
14 Bottle Carving
15 Box Casket
16 Branding iron Catwalk
17 Broken glass Chair
18 Bucket Chandelier
19 Candle Charcoal bin
20 Candelabra Chasm
21 Cards (playing cards) Chest
22 Chains Chest of drawers
23 Claw marks Chute
24 Cleaver Coat rack
25 Clothing Collapsed wall
26 Cobwebs Crate
27 Cold spot Cupboard
28 Corpse (adventurer) Curtain
29 Corpse (monster) Divan
30 Cracks Dome
31 Dice Door (broken)
32 Discarded weapons Dung heap
33 Dishes Evil symbol
34 Dripping water Fallen stones
35 Drum Firepit
36 Dust Fireplace
37 Engraving Font
38 Equipment (broken) Forge
39 Equipment (usable) Fountain
40 Flask Furniture (broken)
41 Flint and tinder Gong
42 Foodstuffs (spoiled) Hay (pile)
43 Foodstuffs (edible) Hole
44 Fungus Hole (blasted)
45 Grinder Idol
46 Hook Iron bars
47 Horn Iron maiden
48 Hourglass Kiln
49 Insects Ladder
50 Jar Ledge
51 Keg Loom
52 Key Loose masonry
53 Lamp Manacles
54 Lantern Manger
55 Markings Mirror
56 Mold Mosaic
57 Mud Mound of rubble
58 Mug Oven
59 Musical instrument Overhang
60 Mysterious stain Painting
61 Nest (animal) Partially collapsed ceiling
62 Odor (unidentifiable) Pedestal
63 Oil (fuel) Peephole
64 Oil (scented) Pillar
65 Paint Pillory
66 Paper Pit (shallow)
67 Pillows Platform
68 Pipe (smoking pipe) Pool
69 Pole Portcullis
70 Pot Rack
71 Pottery shard Ramp
72 Pouch Recess
73 Puddle (water) Relief
74 Rags Sconce
75 Razor Screen
76 Rivulet Shaft
77 Ropes Shelf
78 Runes Shrine
79 Sack Spinning wheel
80 Scattered stones Stall or pen
81 Scorch marks Statue
82 Scroll (nonmagical) Statue (toppled)
83 Scroll case (empty) Steps
84 Skull Stool
85 Slime Stuffed beast
86 Sound (unexplained) Sunken area
87 Spices Table (large)
88 Spike Table (small)
89 Teeth Tapestry
90 Tongs Throne
91 Tools Trash (pile)
92 Torch (stub) Tripod
93 Tray Trough
94 Trophy Tub
95 Twine Wall basin
96 Urn Wardrobe
97 Utensils Weapon rack
98 Whetstone Well
99 Wood (scraps) Winch and pulley
100 Words (scrawled) Workbench

Stairs

Random Stairs
d20 Stairs
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

d10 Encounter Template
1-2 Battlefield Control
3-4 Commander and Troops
5-6 Dragon's Den
7-8 Battle Lines
9-10 Wolf Pack
Battlefield Control

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.

Commander

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.

Beast's Den

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.

Battle Lines

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.

Wolf Pack

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.