The Gobman Show

[OmSwaOperations]

So here's the idea:

• The PCs are goblins, who live in a tiny underground settlement.
• The settlement is part of a sprawling network of caves, chambers, traps, lairs, etc. inhabited by many (small settlements of) odd creatures.

Various elements of the environment are "off"/artificial:

• The ecology of the dungeon isn't sustainable, and depends on constant "restocking" by semi-mythical "dungeon masters" who teleport creatures into the dungeon, reset traps, etc.
• The architecture of the dungeon is a mishmash of styles. Some sections have a coherent theme, but there is no unifying history or purpose tying them together. Sometimes, entire areas of the dungeon mysteriously vanish, are reconfigured, or are enlarged, causing earthquakes.
• No creature in the dungeon remembers or knows of an external world. The goblins themselves think their settlement has always existed down here - that, in fact, they are the only goblins in existence.

The solution to the mystery is as follows:

• The dungeon is a kind of zoological reserve/entertainment show/terrarium for a civilisation of trans-dimensional Giants and their pneumatic servant-golems (the dungeon masters).
• The Giants wipe the memories of creatures introduced to the dungeon, and use scrying to follow along with the conflicts of its inhabitants. This is their favoured entertainment.

The gameplay loop is as follows:

• Explore the dungeon to help grow and protect your vulnerable goblin settlement.
• Encounter new PC options by befriending settlements with other races.
• Discover the truth behind the dungeon and decide whether or not to reveal it to your fellow goblins (easiest)/ personally stage an escape (hard)/ stage an escape for your tribe (super hard)/ stage a mass breakout (next to impossible).

The only difficulty here is that I don't want to write a 300 room megadungeon from scratch. Does anyone have any suggestions as to something that would provide a good framework for this type of play?

[HumanFighter]

I think that sounds like a really fun idea! Unfortunately, I don't know how I can help you figure out the 300 room megadungeon thing. Maybe just draw some maps, a few rooms at a time? You said the dungeons change around a lot, so maybe you don't have to do 300 rooms all at once. Maybe try finding a random dungeon generator online?

[caden_varn]

I certainly wouldn't worry about mapping the whole thing now.
Start with the local environment - who are the goblin's immediate neighbours? Sketch this out (just draw circles on paper for each settlement & link them with lines for now). Maybe add some notes on the hazards between each.

Then have a session 0 for character design/creation where you give the players a bit of spiel on what they know & get some feedback on what/where they want to go first. Then you have a target to design a smaller section for their first few sessions. (Make sure you leave a week or so between session 0 & 1 to give you time to do this).
If things go well you can expand this as they make new plans. The key for me is make the players aware that you write based on what they want to do next - and always leave some time at the end of the session for the group to tell you what their main goals will be in the next session/section so you can plan appropriately.
This way, if interest fizzles out after a while you haven't wasted a lot of work.