I’ve had an idea floating around in my head for years that stems from me asking too many questions about the minutia that makes up the world in which DND can take place.  Questions like:
What are the odds that a party picking up a contract will survive?
Does anyone make a profit when adventurers die in a dungeon?
Who makes the traps in these dungeons?

A fun idea came into my head years ago of people in the world taking bets on the parties willing to take on some of the crazy contracts posted in the local adventurer guilds.  Gambling happens around everything in our world, why not this?  Would this lead to people trying to increase the odds by giving adventurers gifts of magic items or training?

This thought experiment leads to the reverse idea coming into sight.  Who builds the dungeons, inspires (or pays) creatures to inhabit them, loads them with traps, and maintains said traps?  Imagine a large metropolis, filled with the best shops in the kingdom, the biggest thieves guild, wizard schools, bardic troupes, and mysterious dungeons, catacombs, sewers, haunted mansions, and more.  Work is easily found for adventurers in many adventurer guilds, and the city seems to be brimming with problems to be solved.  Although the players don’t know, they are being watched by many eyes.  Some in the city want them to succeed, betting large sums of money in their favor and offering aid in the quests.  Others want to see them perish.

For some of the rich and powerful in the city, it has become too mundane to simply bet against adventurers.  A very diverse group has come together to construct the most devious of dungeons.  They secretly employ teams of the best trapmakers, make unholy alliances with extraplanar beings, summon hordes of the undead.  Scoring their creations against each other by the skill of the adventurers they can kill, this Dungeon Masters Guild (DMG for short) posts false quests in the guildhalls of the city to entice heroes to their deaths.

I’m looking to continue the thought experiment.  What ideas for Dungeons Masters, dungeons, traps, quests, plots, enemies of the DMG, and allies of the DMG can you think of?  This story can easily provide material for an entire 20-level campaign ending in a showdown with the DMG itself.

Many mobile games are based around this concept, so I would run with it: Build a dungeon against inavders. Surprise and the unknown is always a wonderful way to trap players. Traps come in all varieties to include contact-, proximity-, or time-based. Monsters can be plentiful, singular yet powerful, conveniently placed to their advantage, or even illusionary (maybe also sitting on a trap). Even though it kills the pacing of the game, players should feel as though every room is a deadly puzzle that requires more than spamming skill checks to get through.

Hmm.....  can I ask something?   Are you taking the whole dungeons-are-alive-and-make-monster route here?  That's what it sounds like.   D&D, by default, uses the opposite (monsters make dungeons as their bases to threaten civilizations), but let me talk a bit about my impressions of the former.

 There's a lot of stories and games built around the idea that "dungeons" are basically specific magical creations that exist to create rooms and inhabit  them with monsters and traps.  Usually, in these stories, the answer to "who dun it and why" is either "a wizard" or "a god."  And the reason is usually for something along the lines of testing humanity (and possibly other sapient races) so they grow stronger, or the like.  Another rather popular idea is that the dungeons serve to as gathering points of magical impurities, which then manifest as monsters.

What's notable about these stories is that they usually have dungeons as the background, with a strong focus on Slice of Life interactions.  Dungeon creation becomes a cornerstone of economy, and there's a focus on how that effectively serves as mining.  Or, another way they're used?  Dungeons become glorified training montages while the actual threat exists outside of the dungeon itself, or threatens the dungeon's purpose as a source of livelihood. 

 So, insert a bunch of playful nobles who are setting up this complex artificial dungeon that solely exists to push the adventurer's skills to the limit (*cough* Tomb of Horrors *cough*).  Dungeons in this kind of story aren't set to threaten kingdoms, but be mined for treasures.  I'm assuming that's still true?  Building something that would directly threaten the kingdom sounds like the kind of thing that would massively backfire with the simplest Commune spell and angry gods, which would result in a rather extreme response from certain quarters.

Anyways, adventurers come to the dungeon-mine to look for riches, and...do their job?  I'm assuming this DM Guild is going to be smart enough to make the treasures worth the danger.  So, other than this being an extreme form of underground fighting rings... what's the conflict here?  The motivation?  Survival in a new dungeon to mine for treasures.  Is there anything else?  Then what?  You find out about the nobles, and...  do what?  Is someone, somehow, forcing you to dive into the dungeon?  What stops you from just walking away?  The DMG is supposed to be these big-bads, but .... why fight them?  Are they stealing souls for some evil ritual, or something?   Do they need to be stopped with violence, or just exposure?

"This thought experiment leads to the reverse idea coming into sight.  Who builds the dungeons, inspires (or pays) creatures to inhabit them, loads them with traps, and maintains said traps?  Imagine a large metropolis, filled with the best shops in the kingdom, the biggest thieves guild, wizard schools, bardic troupes, and mysterious dungeons, catacombs, sewers, haunted mansions, and more.  Work is easily found for adventurers in many adventurer guilds, and the city seems to be brimming with problems to be solved.  Although the players don’t know, they are being watched by many eyes.  Some in the city want them to succeed, betting large sums of money in their favor and offering aid in the quests.  Others want to see them perish."

The Cube: "

Holloway: It's all the same machine, right? The Pentagon, multinational corporations, the police. If you do one little job, you build a widget in Saskatoon, and the next thing you know, it's two miles under the desert, the essential component of a death machine. I was right! All along, my whole life, I knew it! I told you, Quentin. Nobody's ever going to call me paranoid again! We've gotta get out of here and blow the lid off this thing!

Worth: Holloway, you don't get it.

Holloway: Then help me, please. I need to know!

Worth: This may be hard for you to understand, but there is no conspiracy. Nobody is in charge. It, it's a headless blunder operating under the illusion of a master plan. Can you grasp that? Big Brother is not watching you.  "

and 

"

Quentin: Why put people in it?

Worth: Because it's here. You have to use it, or you admit it's pointless.

Quentin: But it, it *is* pointless.

Worth: Quentin... that's my point. "

If you build it, they will come?
Damn right I would - I am old school enough to enter a dungeon "because it's there" and modern enough to know that I mostly skip the quest dialogue in MMOs.
"What do you want me to kill, and how many of them?"
The latter is probably because most of the "quests" are so un-inspiring. Kudos to Neverwinter for somehow avoiding this with good writing and a desire to go beyond WoW.

Thanks to IMDB for the above quotes.

Now I need to go and score some steroids....
....I'll be back.

The above reference reminds me of a vault from Fallout: New Vegas. Abandoned, political posters litter the walls declaring that people vote for the most morally reprehensible candidate possible: "Sally has embezzled millions, Vote Sally", or "Jim is a pinacle of moral standards, vote Bill".

The candidate voted for vault overseer was taken to a mysterious chamber and sat in front of a tv. Turns out the whole vault was a social experiment to see if people could be convinced to sacrifice their own under the impression of widespread safety (Greater Good). When the new overseer was sat down, the truth was revealed and they were executed. Everything ended when someone decided to say "no" and everyone realized it was a hoax.

If this campaign based around a gauntlet of death kicks off, I will gladly hop in.

This gives me a lot to think about.  I like the idea of two models: the dungeons being the means and the dungeons being the ends.  I hadn't quite worked out how they become the big bad in this scheme, but the collection of the souls of those lost in their dungeons sounds like an interesting pitch.  This doesn't need to have been the original reason that the DMG started, but it has become its main purpose today.  Maybe not all members know this is being done.  Maybe the collection of souls is being done in secret.  Maybe it's just a small group within the guild being influenced by the minions of an Elder God.

I want to leave the creation of each dungeon open to the minds of their creators.  I want the style to cover the gambit from warriors filling a cave with their strongest allies to craftsmen making every room just one piece of a large death puzzle to wizards conjuring up beings from various planes.  At this point, I'm coming up with a list of DMs.  Each can have many dungeons depending on their power, wealth, and skill.  Each can have different motives and alignments (though I cannot figure out a reason for a good character to participate).

Of course from the players' side, there must be treasure to be found in each dungeon.  The risk must be worth-while.  Each quest posted in the adventurer guild can't simply be: go explore this dungeon.  To continue to entice adventurers without drawing suspicion, the DMG will need to come up with cover stories for each of their dungeon quests.  I'd like ideas on that as well.

You know that at some point, the players are going to want to build their own dungeon (and probably force the BBEGs/nobles/Damon Killian to participate.)

In my experience, PCs pretty much almost always want to start building their own strongholds.  Wizard towers, temples, druid groves, fortresses;  developing your own base is almost second nature in games, I've found.

Fortunately, there's already a number of spells, both in core and Xanathar's, to do just that.  Mainly with clerics and wizards, though converting to other classes isn't too hard.  So, making a dungeon is easy enough to accomplish once the PCs are at a high enough level.  

Quote from ArchitectOfConfusion >>

This gives me a lot to think about.  I like the idea of two models: the dungeons being the means and the dungeons being the ends.  I hadn't quite worked out how they become the big bad in this scheme, but the collection of the souls of those lost in their dungeons sounds like an interesting pitch.  This doesn't need to have been the original reason that the DMG started, but it has become its main purpose today.  Maybe not all members know this is being done.  Maybe the collection of souls is being done in secret.  Maybe it's just a small group within the guild being influenced by the minions of an Elder God.

Quote from Mephista >>

In my experience, PCs pretty much almost always want to start building their own strongholds.  Wizard towers, temples, druid groves, fortresses;  developing your own base is almost second nature in games, I've found.

 

That nesting/fort building behaviour is hardly surprising considering how many PCs start their careers having suffered the loss of almost everybody important in their lives. The paranoia must be strong in a group of 6 adventurers who are all orphaned and then unemployed due to the death of their master even before they roll their first d20.

Who in real life doesn't aspire to own their own home? Maybe less will be willing to admit to wanting a basement dungeon.......
Once you do own your own property, then you can worry about home invasions. Our local council says I have to have planning permission to install a pair of trebuchet on the roof, and I won't get it because then everybody will want them. (Block wars anyone?)

So yes, I agree that while in most campaigns the PCs will be looking to become "landed", in a campaign based around "artificial" dungeons, the DM is all but setting the players up with the expectation that this will not only be achievable, but that it is a desirable climax to the campaign. And being the climax, it has to be awesome. Maybe with a twist that drags them into it against their will.......

I'm waiting for them to bring back level-based incentives for biilding an established landmark residence. Back in AD&D (and maybe later versions, I'm not sure),  certain classes received Followers at lvl 9 with the provision that they build/obtain a stronghold of sorts. Warrior subclasses (Fighter, Paladin, and Ranger), Cleric, and Thief (rogue subclass alongside Bards) all received highly-devoted, lower level/0-level minions that were attracted simply out of a desire to follow their reputable leader.

Fighters with a stronghold got 3 tables: Foot soldiers (lvl 0, but ranging about 80-150 strong), a unit of elite warrors (lvl 1-2, numbering 15-30), and a Lieutenant (Fighter lvl 3-6 with gear). Paladins received a slightly smaller, though religiously fanatical, following. Rangers received only a few followers, but included animals, druids, other rangers, etc.

Clerics' followers were typically a small (20-30) group of proto-knights and minor clergy to form the basis of a strong church location. Always good to have if you need a safehouse to recouperate.

Thieves were expected to start a thieves' guild and got a collection of thieves, bards, sub-humans (possibly even some lycanthropes), thugs, etc.

I love the above ideas because it adds more than a bit of beefiness for characters in a ruleset that made you very vulnerable on a regular basis. It added the ability for characters to provide regional influence and protection, not just in one specific site or scenario. A Thief's following can hather money and intelligence, a Fighter's following can act as mercenaries, envoys, or protection. Clerics can leverage their church following for diplomacy, healing, etc. (imagine a 10-day travel and having someone with heals waiting at the end of each day).