Another experimental idea-generating method.
You could use this for campaigns, hex-maps, cities, etc. I happen to need a lot of dungeons, so I'm going to use it for a dungeon in this case...
(Note: this worked pretty well so I might use the dungeon in this example, so if you're playing in my game in LA don't read it...)
Start with a random or hastily-thrown-together dungeon (or city, or list of campaign elements, or hex-map locations or whatever).
I'm gonna use a random dungeon and I'm gonna populate it using the instadungeon tables...
(unlike the actual complete instadungeon rules, this method is slow, so if I'm taking the time here I might as well use a genuine dungeon rather than the flow-chart-like maps that the instadungeon method produces)
1 soldier-type monster riding brute
2 brute monster staked down
3 locked and trapped door
4 soldiers guarding weapons/treasure/boss
5 3d6 soldier-type monsters
6 locked door, pick-crusher trap
7 extra tough lock
8 major villain
9 sleeping soldier-type monsters (barracks)
10 1d4 soldier-type monsters
11 locked & trapped door
Run down the list of things you randomly or hastily generated and add one detail to each thing. It doesn't have to be an amazing detail, just some detail.
I'm going to start with the major villain in room 8. It's behind a secret door and a portcullis, so I'm going to decide it's a prisoner. It's creations/servants have risen up against it.
Then I'm moving out from there...the soldiers guarding it in 4 are...(looking for something I haven't used lately)...thornchildren (they're spiky botanical-monsters from Vornheim).
Now room 6 has a pick-crusher trap (I'll say it's the west door near the guards) since that technology seems a little beyond sentient roses I'll say the dungeon was built by someone other than them and they are infesting it...
Room 7 has an extra tough lock--I'm gonna say it's both locks to room 7 since that makes more sense. And the locks are tough because...they're choked and grown-over with pieces of dead thornchild.
Room 9's full of sleeping guards--thornchildren? No, let's say they're some monster that tends or "grows" them. It will come running if there's a ruckus in room 4.
Room 10--3 more thornchildren--what are they guarding in room 11?
Room 11--locked and trapped door...because there's treasure in here.
3 Ok, so let's say both these doors are locked and trapped.
1 & 2 have brute monsters. Why would they be in here? Probably experiments. Something that someone tending/creating thornchildren would also be interested in...ok, let's say they're gibbering mouthers. And the one being "ridden" is being experimented on by some sort of humunculus or other igor-ish assistant.
...And last we have room 5. It makes sense if this is the first room the PCs see, which means the locked door and the guards make sense and it means this dungeon is probably below ground as opposed to being a building. I'll also roll for how many guards the room has...
1 soldier-type monster riding brute g. mouther being experimented on by "igor"
2 brute monster staked down gibbering mouther
3 two locked and trapped doors
4 thornchildren guarding prisoner
5 3d6 soldier-type monsters first room 10 guards
6 locked door, pick-crusher trap built by original architect
7 extra tough locks grown over w/spiky vines
8 major villain--prisoner
9 sleeping soldier-type monsters (barracks) tends thornchildren
10 1d4 soldier-type monsters 3 thornchildren
11 locked & trapped door treasure
Repeat step two for each item, in order, until the dungeon is interesting to you.
1 soldier-type monster riding brute g. mouther being experimented on by "igor" room is full of chemicals/potions with bizarre effects
2 brute monster staked down gibbering mouther it is an aggregate of tortured souls
3 two locked and trapped doors room appears empty
4 thornchildren guarding prisoner can't tell humans apart, they identify their master using a creepy question
5 3d6 soldier-type monsters first room 10 guards the guards are animated objects of some kind
6 locked door, pick-crusher trap built by original architect the villain who is locked up in the prison
7 extra tough locks grown over w/spiky vines this room used to be the villain's bedroom
8 major villain--prisoner a succubus
9 sleeping soldier-type monsters (barracks) tends thornchildren leader of the revolt against the succubus
10 1d4 soldier-type monsters 3 thornchildren if all 3 sing simultaneously they generate a sleep spell
11 locked & trapped door treasure 4000 gp, some random items and the key to the prison
1 soldier-type monster riding brute g. mouther being experimented on by "igor" room is full of chemicals/potions with bizarre effects "igor" is a small girl in velvet--an immature demon
2 brute monster staked down gibbering mouther it is an aggregate of tortured souls it is inside a thaumaturgic circle--like the other mouther, it will lash out at anything near it--including other monsters
3 two locked and trapped doors room appears empty room used to be a parlor of sorts, secret door is behind a painting. The painting is a disturbing-looking and semi-animated portrait of the succubus, however, so PCs, hopefully, will be scared to mess with it.
4 thornchildren guarding prisoner can't tell humans apart, they identify their master using a creepy question "What happened to your dear sister?""Baked in a pie and sold to starving salesmen!"(the gibbering mouthers say this, among other random phrases. this is the only phrase that could be a logical answer to this question. they also give other hints--make a list of 7-12 mouther phrases to read off in a babble--practice pretendign you just made it up so PCs don't know they're significant)
5 3d6 soldier-type monsters first room 10 guards the guards are animated objects of some kind they are little cherub statues that look like Falconet's cupid from the Louvre--only all are damaged in some way--wing cracked, arm handless, etc. They come in "hear no evil" "speak no evil" and "see no evil" varieties and can make you deaf, mute, or blind respectively--with a kiss. They also try to choke you by shoving their hands and feet in your mouth.
6 locked door, pick-crusher trap built by original architect the villain who is locked up in the prison actually, it's more of a finger-amputator than a pick-crusher. The fingers appear in a finger-sculpture in hallway between 7 and 3. All the traps are amputators of one sort or another. All the locks are large and ornate and obvious and look like locks on diaries.
7 extra tough locks grown over w/spiky vines this room used to be the villain's bedroom it's full of pyxides containing small, moaning "mouthers" in jars and is done in a predictable opulent-infernal-floral motif.
8 major villain--prisoner a succubus will appear to be a harmless female alchemist interested in exotic plants.
9 sleeping soldier-type monsters (barracks) tends thornchildren leader of the revolt against the succubus another immature demon--this one looks like a fetus
10 1d4 soldier-type monsters 3 thornchildren if all 3 sing simultaneously they generate a sleep spell this room is an elaborate, fountained bath, it is half full of black (soulless) blood, victims may drown in it. Will come back as soulless undead.
11 locked & trapped door treasure 4000 gp, some random items and the key to the prison this door (and all trapped doors in the dungeon) require singing a specific tune to get past. The mouthers sing all the tunes at one point or another. The amputation is not mechanical, it is magical--the first to touch a door without singing the appropriate song simply loses the limb in question,
And there it is. I think I might add a few more empty rooms to the final version (the instadungeon tends to overpopulate dungeons) and maybe a library with books on exotic horticulture, and maybe a torture garden...