(Preamble you can skip)
You're DMing. The PCs go down into a dungeon. But you don't have one...
So...Random dungeon generators. Some basic principles (using the categories I made up here):
Fast, easy-to-use, complete random dungeon generators do exist. Mostly on-line. However: these dungeons are either totally random (Room 1: Gnolls! Room 2: Ghosts!) or have elements taken from a list of thematically similar elements (Room 1: Ghosts! Room 2: Spectres!).
Fast, easy-to-use, complete random dungeon generators for dungeons that make some sense and are kinda original do not.
(Randomly picking from a list of pre-existing dungeons is not usually an acceptable solution because:
1-it takes just as long to prep a pre-existing scenario as think up one, and
2-if you liked a module enough to have prepped it, you'd probably have put it somewhere on the map by now)
Slow, easy-to-use, incomplete/inspirational random dungeon generators do exist. These are essential DM-prep aids and are not designed to be reliably and repeatedly used to improvise during a game.
Fast, easy-to-use, complete random dungeon generators for dungeons that make sense and are kinda original (that is: fast breeding generators for dungeons) are probably, in the abstract, impossible to make, since making a whole dungeon fast would require a computer, doing it so it makes sense would require literary creativity beyond the power of a computer, and doing it with random rationales instead of derived ones would essentially make it incomplete since the DM would still have to make the pegs fit the holes and figure out how A led to B in order to make the dungeon make sense.
The best we can probably do, to give the DM a during-the-game random dungeon generator for dungeons that make some sense is a sort of half-measure.
Here's my idea for such a half-measure:
A dungeon generator that functions as a simple, complete generator for all the elements of a single dungeon room (the first one the party enters) but also gives reasons for everything in that room being the way it is. These different reasons can then be used by the DM to understand what's going on in the rest of the dungeon and populate its rooms accordingly, at least until the session's over and the DM has time to prep again.
The principle here is that giving a DM an incomplete generator for a whole dungeon in the middle of a session doesn't help, but sort of giving him/her a "Drip-feed" of information one piece at a time,w hen needed, will help him/her slowly improvise a dungeon.
The generators do not have to cover all possibilities for what could happen in a dungeon room, just a wide enough range for that first room. Assume the real creative heavy-lifting will still have to be done by the DM some point down the line. This generator is just that first dose of morning caffeine.
If this seems a little vague, hod on, because I get real specific soon...
There are basically four parts to a dungeon room:
-Encounter: The major thing that is in the room. A monster, a puzzle, a device, whatever. Some rooms don't have these, obviously.
-Exits: usually doors or doorways, these are things you have to deal with to get in or out of the room.
-Decor: What it looks like and incidental furnishings, including light sources, etc.
-Layout: Physical size and shape of the room.
I am gonna assume that if we can generate Encounters and Exits and reasons for them, then the Decor and Layout have a good chance of being strongly implied by one of the reasons we got for the Encounters and Exits. (Like: if we figure out the room has a cursed altar, then we know we've probably got candles and maybe pews, etc. and the room's kinda big.)
So: Encounters, Exits, and reasons for them and nothing else. To make things easier we're going to assume this first room:
1) Has an encounter (it'll give the DM time and fuel to start imagining the rest of the dungeon)
2) Has exits in the form of doors (i.e. this first room will not be one of those "apparent dead ends but actually the exit is through the yellowish puddle on the floor" rooms)
Exits are easier so we'll do that first, we'll do encounters another day:
In the rationales for these results, I'm going to use the following terms...
Architects: whatever culture or individual built the place in the first place
Inhabitants: whatever cultures or individuals live there now
Intruders: individuals (like the PCs) who just came down into the dungeon recently to loot it or whatever
Assume each room has whatever portal the PCs came in through plus d4 others. Since this is just the first dungeon room, I'm going to assume the exits are all just doors (i.e. the possibility of a dead end). Roll once for each door or once, period, and apply the result to all the doors.
So, 100 Dungeon Doors And Why They're There:
1-Trap, primitive/simple. Because intruders are looking for something in here and rigged it up because they don't want to be disturbed.
2-Trap, primitive/simple. Because the inhabitant culture is primitive/simple.
3-Trap, primitive/simple. Because the mechanism is old and no longer works as well as it used to.
4-Trap, primitive/simple. Because ____________
5-Trap, primitive/simple. Because____________
6-Trap, primitive but magical. Because intruders who have a magic-user with them are in here and don't want to be disturbed.
7-Trap, primitive but magical. Because the inhabitant culture is primitive but has shamen/priests.
8-Trap, primitive but magical. Because it was designed to keep out vermin or children, not tough guys like the PCs.
9-Trap, primitive but magical. Because _________
10-Trap, primitive but magical. Because_________
11-Trap, sophisticated (mechanical). Because the architect culture was sophisticated and was protecting something of value.
12-Trap, sophisticated (mechanical). Because the architect culture was of a species that would not need to use the door the way a human would.
13-Trap, sophisticated (mechanical). Because the inhabitants hide something of value behind the door.
14-Trap, sophisticated (mechanical). Because ________
15-Trap, sophisticated (mechanical). Because __________
16-Trap, sophisticated and magical. Because the architect culture was protecting something of value.
17-Trap, sophisticated and magical. Because an inhabitant is a crazy wizard.
18-Trap, sophisticated and magical. Because the architecture is alive.
19-Trap, sophisticated and magical. Because __________
20-Trap, sophisticated and magical. Because _________
21-Locked, ordinary lock. Because the inhabitants didn't think anyone would ever come down here.
22-Locked, ordinary lock. Because the inhabitants are too primitive to do any better.
23-Locked, ordinary lock. Because, to the inhabitants, this is an ordinary place with nothing terribly valuable in it.
24-Locked, ordinary lock. Because the real heavy locks are later down the line.
25-Locked, ordinary lock. Because__________________
26-Locked, serious lock. Because the inhabitants are protecting something of value.
27-Locked, serious lock. Because the inhabitants are xenophobes and this place is forbidden to outsiders
28-Locked, serious lock. Because the inhabitants are sophisticated and this is just normal for them.
29-Locked, serious lock. Because ___________
30-Locked, serious lock. Because ___________
31-Locked, magically. Because the inhabitant includes a wizard.
32-Locked, magically. Because this room contains something of special value.
33-Locked, magically. Because a recent emergency int he dungeon has caused an inhabitant to go around and magically lock as many doors as possible.
34-Locked, magically. Because _______
35-Locked, magically. Because _______
36-Locked, puzzle lock. Because the architects designed this place only to admit certain types of individuals.
37-Locked, puzzle lock. Because one inhabitant is crazy.
38-Locked, puzzle lock. Because it wasn't designed as a puzzle lock but the original mechanism
has sort of fallen apart over the years and now is tricky to deal with.
39-Locked, puzzle lock. Because_____
40-Locked, puzzle lock. Because ____
41-False door. Because the architect(s) was(were) eccentric.
42-False door. Because the inhabitants have some ritual reason for needing them
43-False door. Because a spell was recently unleashed in the dungeon that multiplies the facades of things.
44-False door. Because ______
45-False door. Because ______
46-Doorless archway. Because there used to be a door here but it rotted away.
47-Doorless archway. Because this was a residence.
48-Doorless archway. Because the inhabitants removed the door in order to make it into a residence.
49-Doorless archway. Because this was designed as a temple.
50-Doorless archway. Because ____
51-Ornate but unprotected. Because this used to be a temple.
52-Ornate but unprotected. Because this area is dangerous and has been abandoned by most of the inhabitants.
53-Ornate but unprotected. Because ______
54-Ornate but unprotected. Because _____
55-Ornate but unprotected. Because_______
56-Ordinary unlocked door. Because to the inhabitants, this is an ordinary place.
57-Ordinary unlocked door. Because the lock has been broken by recent intruders.
58-Ordinary unlocked door. Because inhabitants have abandoned this place.
59-Ordinary unlocked door. Because the front entrance was someplace the PCs already somehow passed and nobody expected intruders to get this far.
60-Ordinary unlocked door. Because __________
61-Secret door, mechanically hidden. Because the architects hid something of value here.
62-Secret door, mechanically hidden. Because the inhabitants hid something of value here.
63-Secret door, mechanically hidden. Because this room was a prison.
64-Secret door, mechanically hidden. Because _______
65-Secret door, mechanically hidden. Because ______
66-Secret door, magically hidden. Because the architects were magical and hid something behind it.
67-Secret door, magically hidden. Because the inhabitants hid something behind it.
68-Secret door, magically hidden. Because an intruder has magical abilities and is behind it somewhere and does not want to be disturbed.
69-Secret door, magically hidden. Because _______
70-Secret door, magically hidden. Because _____
71-Door concealed behind stuff. Because intruders are behind it and don't want to be disturbed/discovered.
72-Door concealed behind stuff. Because inhabitants forgot about the room and have piled stuff up in this room in front of the door.
73-Door concealed behind stuff. Because this room is semi-abandoned and full of crap.
74-Door concealed behind stuff. Because _____
75-Door concealed behind stuff. Because _____
76-Accidentally/organically "trapped"--the architecture falls apart in a dangerous way when you attempt to open this door. Because it's old.
77-Accidentally/organically "trapped"--the architecture falls apart in a dangerous way when you attempt to open this door. Because the inhabitants know never to use this door and so use it as a sort of intruder alarm.
78-Accidentally/organically "trapped"--the architecture falls apart in a dangerous way when you attempt to open this door. Because recent fighting int he complex has fucked it up.
79-Accidentally/organically "trapped"--the architecture falls apart in a dangerous way when you attempt to open this door. Because __________
80-Accidentally/organically "trapped"--the architecture falls apart in a dangerous way when you attempt to open this door. Because ______
81-Locked but key is in this room. Because the next room is a prison cell.
82-Locked but key is in this room. Because an inhabitant dropped it.
83-Locked but key is in this room. Because only an intruder would be dumb enough to enter the next room and it's a sort of trap.
84-Locked but key is in this room. Because___________
85-Locked but key is in this room. Because_________
86-Door is alarmed or alerts nearby inhabitants/intruders. Because they are tough but not great at making locks and traps.
87-Door is alarmed or alerts nearby inhabitants/intruders. Because it was hastily thrown together by intruders.
88-Door is alarmed or alerts nearby inhabitants/intruders. Because intruders want to shadow the PCs and take their stuff.
89-Door is alarmed or alerts nearby inhabitants/intruders. Because the inhabitants want intruder to come in for some reason,but also want to know when they're in here.
90-Door is alarmed or alerts nearby inhabitants/intruders. Because_________
91-Door has a broken trap. Because it's old.
92-Door has a broken trap. Because it was poorly made by primitive inhabitants.
93-Door has a broken trap. Because it was recently sprung by intruders.
94-Door has a broken trap. Because ________
95-Door has a broken trap. Because ________
96-Door has a broken lock. Because the architects once kept something of value here but the inhabitants took it long ago.
97-Door has a broken lock. Because intruders just picked it.
98-Door has a broken lock. Because a beast just destroyed it.
99-Door has a broken lock. Because the inhabitants are primitive and suck at making locks.
00-Door has a broken lock. Because _________
I leave the remaining results up to Gygaxian Democracy. Write the number of your rationale in the comments and I will add it to the final table.
Naturally, the final generator will also include separate tables for "12 sophisticated mechanical traps", "12 puzzle locks", etc. etc. as well as some examples of possible "architect cultures" and "inhabitants" etc.
The final version of these tables should probably be done as cards or Vornheim-style drop-die charts so that you can get several results fast.