d20 rooms split between d4 floors. Alternatively you got d6 floors with d8 rooms each.
You can expand a dungeon easily but it's hard to fill a dungeon that's too big when you run out of ideas. Start small and don't use up all your ideas in one place.
For each floor take as many random dice shapes as you need rooms and drop em on grid paper. Draw a room around each die. The numbers can be influence size, shape, and/or exits. Even numbers mean empty (no monsters) odd means a monster inhabitant.
Next, connect the rooms. I let the points on the die, the number facing, the orientation to other dice, and my own whim dictate the direction and angularity of the corridors. Remove each die as you finish drawing the connections, marking rooms that have monsters with some sign
Look at what you have so far. Are there any choke points, issues, improvements, or features or ideas that jump out? Write down all your impressions stream of consciousness on a separate sheet of paper. Make any adjustments to dungeon layout now.
If you had any ideas for room keys start writing them. You can be verbose if you like but try to trim them down to a few sentences max as you continue iterating. Forget worrying about being good or fun at the table, just have fun right now.
Remember the golden rule: quit and come back if it stops being fun.
TIP: set yourself a timer, say 15-20 minutes. Try to finish a whole floor before the timer ends. If you stop and you still have some ideas going just let it be and come back to it. You'll jump back into the flow quicker next time. If you run out of time just erase the extra rooms or fill them with monsters, statues, collapsed columns, furniture, mushrooms, robot parts, bottomless pits, and rivers of acid.
Theme
The organizing idea of a dungeon is the theme. Each dungeon should have a principal theme, and each floor could have a variation of that theme. You may or may not have an initial theme at this point. If not, roll on the spark table below for ideas. To make a variation roll on one or both spark tables again and smash the result with the previous theme.
#rolled | element 1 | element 2
1. | Military | Fire
2. | Famine/plague | Earth
3. | Graveyard | Water
4. | Factory | Forest
5. | Experiments| Sky
6. | Grandeur | Galactic
7. | Melancholia | Caves
8. | Medicine | Hollow
9. | Forlorn hope | Swamp
10. | Crystal | Vapor
11. | Ancient Magic | Conjoined
12. | Solitude | Stone
13. | Primordial | Poison
14. | Prison | Building
15. | Beasts | Withering
16. | Weather | Knowledge
17. | Machines | Mutated
18. | Mushrooms | Hidden
19. | Precipices| Separated
20. | Hallowed | Organs
Filling the rooms
For each monster room, roll a monster.
For each empty room, roll for contents:
1-2. Really empty
3. Really empty, with treasure
4-5. Trick/Trap/Obstacle
6. Trick/Trap/Obstacle, with treasure
Decide on the contents, whether it's random bric a brac or traps, based on the theme. Here's another spark table for room contents. You can throw on the first table once for a simple usage, twice for a "what was it originally? what was it now?", the same on the second table for more ephemeral ideas, or combine the two and even mix with the first table to go really far out. The second table is good for trap effects.
It can help to take the spark you roll and free-associate some names based on it, and use that to get an idea for the room. Example: for "Abandoned Drift" in a dungeon whose theme is "Melancholia Poison" you could call the room "Prison of Oaks" "Void distemper" "Revolving catastrophe" "Slime warren" "Ocean of Dreams". You might roll one more spark element to help break a block, but avoid rolling on the tables a bunch of times.. all the extra detritus just muddies the waters.
Remember to just take a break if you feel a serious block coming. Many times if you quit before the ideas stop all together it'll start flowing again more quickly.
Try to keep a description of the room itself to a single sentence! Remember that 15 minute timer? You might be the kind of person that shuts down when the pressure is on. It can help you as a person to practice working through those feelings.
Oh, sorry, did you think this blog was only about d&d? Haha.
Sorry, here's that table:
#rolled | element 1 | element 2
1. | Barracks | Gravity
2. | Apothecary | Vaporized
3. | Workshop | Evoke
4. | Ballroom | Decrepit
5. | Leisure | Drift
6. | Jail | Sewage
7. | Library | Crushed
8. | Storage | Ransacked
9. | Judicial | Overrun
10. | Foyer | Sealed
11. | Refectory | Unstable
12. | Office | Split
13. | Clinic | Contaminated
14. | Atrium | Buried
15. | Agriculture | Dissolved
16. | Disposal | Deluge
17. | Mine | Torched
18. | Abandoned | Forgotten
19. | Mistake| Mistake
20. | Economy | Temporary
If there's rooms containing monsters next to each other consider making them a faction or at least allies. Decide what they're doing in the room and what nearby rooms they know about/have influence over. Give them things they want, as well as problems and enemies. A single room entry might look like this:
Room 6 - Prison of Oaks
12 blind mushy mushroom men make out with rotting trees growing thru cracks in walls, fed by a continuous light cast on a brass idol of a monkey. The monkey idol is burning hot to the touch. The mushroom men are drowsy/drunken and barely hostile to interrupters. In the middle of each is a blue crystal worth 50 gp.
Once you get the first draft done go over it again, see if any new ideas come up. Next, cut out stuff you hate. Don't be afraid to just leave some rooms totally empty. Add some locked or secret doors, extra corridors, dead ends, more dangerous obstacles, weird effects, highways that connect disparate sections, flooded or caved in areas, alternate entrances, and elevators/stairs/chutes that skip whole floors forming shortcuts.
How much treasure should you put in? Here's my formula:
( Number of expected players * dungeon floor * 2000 + 20% )
I rarely though sometimes make treasure in the form of coins and gems, though that can have some great old school flavor. Mostly it's furniture, weird junk, or pseudo magical junk that players often walk right past.
Half of it is in monster possession, half of what remains is hidden where nobody would look, and the rest is just laying around under/in stuff, or is heavy or bolted down.
Oh yeah last thing make a d6 or d8 encounter table for each floor. You might save deciding what monsters to use until you get your table, or draw the monsters in the table from what you already keyed, or pick totally new monsters for the encounters. I like my encounter tables to have one or two entries from main dungeon factions, then the rest be unique encounters.
The rules for making monsters in Worlds Without Number is great for when you're feeling dumb. Actually WWN is just great.
(PS All art is made by AI because I'm lazy as fuck)