I really hate useless history in setting material. That’s information that players will never discover unless it is read to them in a boring monologue. Then again, I just listened to a podcast where somebody says that the warehouses now filled with artists and lofts are there because traditional shipping and warehousing was replaced by containers. I imagined an Orientalist bazaar in the carcass of a fallen civilisation and thought, this is D&D!
But how to create this? I need a handful of layers. Each historic layer is identifiable by architecture, providing early warning signs to players, as well as signalling the kinds of traps and treasures to be found. Over it all a sequence of immigrations from the top to the bottom, letting players interact with contemporary dangers as well as older, established powers. Say, four layers, four immigration waves. Perhaps the orcs did not reach the deepest levels, perhaps there are no astral gates and their Grell invaders at the surface, so we won’t have to think about all combinations, but there will be enough variation nonetheless.
Maybe take a sheet of paper, draw four interlinked circles for the historic layers, and on top of that, another four interlinked circles for the immigrations. Then draw a point crawl on top of that and let all the locations be influenced by the circles they are in – one or two historic layers for architecture, traps, treasure, items, and one or two immigrations for current denizens.
Instant lore and theme for your megadungeon or wilderness?
I guess you could say I want to create an underworld that feels like it might have been the result of How to Host a Dungeon without actually playing the game.