Where do dungeons come from? How many undead-infested tombs can there really be...

This. Underdark was a super cool idea that didn't get the push it needed, in my opinion. Nameless eldritch horrors waiting for those who go to deep only adds to the flavor.

OP just look at the "Lost Cities" page on Wikipedia, look at some of the crazy ruins in Cappadocia, look at pictures of the Roman era ruins scattered all over Europe.
Hell, look at at the abandoned mills and factories and shit in the southern US that were built back in the 1800s. There's a famous one in Italy but you can find those everywhere out innawoods.

Add some magic and a few goblins and boom, dungeons.

>under cities
or under where cities were

Not!Rome found out about dragons ruling their not!China. They lost their shit and proceeded to dig underground vaults where one could survive a giant flying beast. The amount of money spent was one of the reasons it is gone. The vaults full of relics remain.

The dragons never cared much about the whole thing.

The rest of the thread has things I also use, except for paleotocas:
en.wikipedia.org/wiki/Paleotoca

They're also not gonna be filled with monsters and/or treasures. If they're located directly under an active city then they're used for something, and monsters wouldn't be allowed to enter in the first place. or would quickly be driven out by the city guard. If they're abandoned but the city above isn't it would still be considered a hazard for monsters to inhabit them and as such the city guard would still regularly patrol the underground tunnels, and any treasures left down there would have been scavenged long ago by those very guards or thieves. If the tunnels were somehow sealed off to prevent potential monsters from reaching the city and any treasures were left down below they would still have been plundered years ago by thieves.

The point is, even if dungeons can be considered realistic, the adventurer profession isn't.

dungeons are actually a strange type of entity. They grow as seedlings beneath the earth and send up entrances to the surface. Prey is lured in by the promise of shelter, prey or treasure. The dungeon feeds off the death of anything inside it, be they human or monster. The older the dungeon is the more it extends itself both above and below ground. If deprived of food long enough they die and the structure begins to decay and eventually collapse.

That thumbnail is disturbing, at least if you just glance at it when it's scrolling past.

Dungeons are created and stocked with the treasure from the sacrifice every ten years to appease the gods.

Dungeons are spontaneously generated in the same way medieval people believed life was, when the conditions are exactly right.

Dungeons are actually the underworld, where all lost things - peoples, treasures, architecture - eventually surface.

The planet is a living being, and dungeons are its blood vessels, nerves, and maintenance tunnels all wrapped up into one.

Dungeons occur when our universe touches an adjacent universe - whatever is present is destroyed (hence the hollow tunnels) and strange things pour through and get stuck.

Dungeons are created for gladiatorial entertainment by perverse and super-powerful entities who act as their Masters. Bait the tunnels with treasure and fill the labyrinth with deadly monsters, obstacles, and puzzles for your own amusement as people struggle and fail to get rich overnight.

This picture makes me uncomfortable.

Dungeons are actually created by colonies of microbes and fungi that have the blueprints for the optimal amount of space and airflow needed for their underground survival and reproduction hardcoded in to them. The denizens just move in after them.

Right you are, Ken

they're a necromancer's/wizard's storage areas.
That's what happens when magic users are able to summon things and single-handedly ruin economies.

>Elder Scrolls's mechanical ruins were made after an entire race (barring one or two) were vaporized during a sudden extinction event of their kind

>Ayelid ruins were when people from another continent were driven out and rendered unusable thanks to magical energies attracting monsters and raising undead

>Nord barrows are just cursed to begin with because they're a bunch of retards that don't know how to bury their dead without them reanimating on their fucking own

>Undead nigger storage

Any cave sufficiently deep, dark and lonely spawns an entrance to the underworld eventually, just like any sufficiently large and wild wood can be used to access some kind of sylvan otherworld.

Dwarves and other peoples that live in dungeon-prone environments have an annual festival where they make a point of bringing light and cheer and noise to every remote nook, just to banish any incipient dungeons. Though in a few places they're deliberately cultivated to exploit the strange creatures and odd artifacts that can be found in the underworld.

>abandoned underground cities
>abandoned subterranean temples and necropolises
>abandoned catacombs
>abandoned fortifications
>naturally occurring cave systems
>ruins of ancient cities
>burrows and tunnel networks dug by underground megafauna
>abandoned sex dungeons that have been turned into regular dungeons
>tunnels dug by guerrillas and bandits to serve as hideouts
>dungeons created by reclusive mages solely to draw people away from where they actually are doing their insane and more often than not morally dubious experiments
>rarely used or mostly abandoned sections of city underground
>abandoned mines
>precursor bomb shelters and bunker complexes that were never used because the the end became so quickly that no one really managed to make it inside
>they were built as a way to stimulate the economy hundreds of years ago, no one knows why but apparently hiring couple hundred unemployed guys to build a purposeless underground network of tunnels and halls was good for economic recovery

>Sometimes the dead just get up and start attacking people for no reason.

>Let's inter them intact, unrestrained, and with all their weapons.

>Nord barrows are just cursed to begin with because they're a bunch of retards that don't know how to bury their dead without them reanimating on their fucking own

It is part of the native charm, just think what Skyrim would be like without billion nordic barrows filled to the brim with draugr, people could go take a shit without having to pay a random wanderer to clean their outhouse from wandering dead first.

Have people becoming monsters to be one of the main causes of "death". Have not only diseases, but also things like sleep deprivation, malnutrition/dehydration, being possessed, certain emotions, being a miscarried baby, etc. be possible methods of someone becoming a literal monster.

Have multiple planes of existence that overlap, so that if there's nothing going on in one there might be something going on in another. This can be either dimensions, or have caverns underground of islands in the sky be common features of the world.

Have the majority of the world be filled with horrible monsters, but have methods for cities and towns to shield themselves (force-fields, burning the evil vegetation, putting runes or certain substances along the town)

Have different regions of the world have certain monsters which are known to be in the area, people in the region have ways to deal with most of the monsters in their region, but one that's more difficult to deal with has had a good breeding season, or unfamiliar monsters from a different region enter the region.

A variety of ancient ruins, you can even have ruins and artifacts suddenly appearing from a civilization that exists on a different plane or from civilization that has intentionally or unintentionally sent things into the future/past.

The land twists and rotates around, like a sped-up version of the continental plates moving.
Because of this, places are put near things that dangerous and unfamiliar, and caverns once isolated and hidden become connected to something.

Once upon a time, a mighty king crushed all the rebellious nobles within his realm and his rivals outside of it until he ruled the entire known world. Nothing was outside of his grasp. But now he was faced with a bunch of warriors and wizards who were itching for a fight but there was nobody left for them to fight, and civil war seemed inevitable. The king then came up with a cunning plan: the best stonemasons and the most brilliant magical minds would work together to create grand constructs filled with the most deadly and dangerous monsters. The dungeons were planned out brilliantly, with "starter areas" where the monsters would be of lower levels and "endgame areas" with monsters of higher levels. Of course, within the dungeon the level of the monsters would also increase the deeper you went into it. This provided a challenge for all the bored warriors and wizards of the realm, and secured the unquestioned rule of this wise king and his descendants for generations to come. Until a party of muderhobos manages to exterminate all monsters in the final Superdungeon of course, then civil war becomes a viable possibility once more.

There are plenty of real-world areas that would serve as undead infested dungeons if you put your mind to it. The two best examples I have;

en.m.wikipedia.org/wiki/Mound_Builders#Mississippian_cultures

The Mississippi Mound-builders were theorized to be a nation based around the Mississippi but were wiped out due to either illness or famine. The mounds they left behind dot the landscape for a pretty far distance, and in a fantasy setting could definitely serve as a wau to have dungeons all across the land.

bbc.com/travel/story/20160309-the-empire-the-world-forgot

The City of Ani, "the city of 1,001 churches", used to be a regional power at the border of Turkey and Armenia, with over 40 cathedrals and a bustling trade hub. It even has a network of caves in the nearby valley and at the base of the hill it rests on, which would make for a fantastic megadungeon: the anvient leaders of this once powerful city, under siege and on the verge of being destroyed attempt to hide their riches and run using tunnels beneath the city. Now people flock there to find these loat riches, and have to contend with not only the denizens of the city and caves, but other adventuring bands as well.

2 words: Skeleton Landscapers

Don't dragons actually have some big great game chess bullshit like that?