My own Secrets of the Nethercity is designed to be as logical and plausible as I possibly could achieve. It's my "masterwork" in terms of Gygaxian naturalism.

-- Excavation is noted as taking place over a long period of time
-- The builders of the dungeon have improvements in their necromantic and alchemic abilities over that time
-- Therefore the danger of the dungeon increases as you get into the deeper (e.g. more recently excavated) portions because the undead buried there are more powerful and better-preserved
-- The dungeon architecture changes over time to match the time of excavation so players can "clue in" to where they are
-- There's a well-described dungeon ecosystem
-- All non-undead found in the dungeon have a reason to be there, a food source, and a water source
-- There's a good reason given that the dungeon hasn't been delved by adventurers

for me a dungeon in the sense we've become accustomed to is a rare thing requiring certain needs be in place.

Lets say i find a boulder with a crack, and this crack leads down into a tunnel that becomes a maze of tunnels that at some point connect to other dimensions entirely, this thing is dangerous, it spits out demons and monsters every so often, so the king, being wise and bearded as kings are want to be, has a huge pit dug and the boulder rolled into it, then encased in a steel locked box.

Bad folks still might want to seek monstrous allies and attempt to rupture the box, so a vault is built around that, then a series of man-trap like structures as one moves away from the vault, and finally a fully garrisoned fort is built atop that...so that should anything evil escape the boulder vault, it has to work its way through traps toward the surface, stopping to count things placed along the way just to distract or slow them, and a force of troops in the garrison above can be poured down atop the escaping evil to push it back. Many a portcullis bemoaned.

This, and very few other scenarios, really do for me the explanation of why what we think of as a dungeon might exist. All dungeons are a crawl or delve that is difficult and dangerous so to a certain extent its designed to keep people out or away from its lowest regions...but to be termed a dungeon proper it must also fulfill the criteria of being a prison of some sort meant to keep something in.

The dangerous portal dangerous artifact angle is the best i can come up with.

Quote from: Marchand on December 14, 2022, 11:43:35 AM
Can't remember the exact reference but somewhere in AD&D1E or B/X there was a mention of abandoned wizards' towers still stocked with their former owners' collections of henchbeings and experimental subjects. Logic would probably require the stocking to reflect a brutal Darwinian sorting-out of the denizens after the original owner vacated the premises. You could have the orc henchmen near the entrance and then the deeper crypts where they don't go.

There is an Alastair Reynolds SF story about rich sickoes who compete to stock collections of rare and dangerous creatures. A fantasy environment could easily have similar. It's just a variant on the abandoned-wizard's-tower theme.

Back in the real world, Silk Road explorers like Aurel Stein were sticking their noses into cave tomb complexes within the last 100 years or so.

Since @amacris didn't mention it when talking about Secrets of the Nethercity, I'll add that ACKS has domain mechanics that encourage even PC wizards to set up a dungeon full of monsters somewhere near their tower and stock it with treasure, hoping wandering monsters set up lairs and breed to become a renewable source of magical research supplies.