Last night my local crew decided, on short notice, that we were going to play Moldvay D&D for a while. Tossing the idea around, we agreed we’d level up after every session and share GM duties (so I guess we aren’t exactly playing Moldvay D&D after all). I proposed a vague outline for the world and everybody signed onto the premise - it’s science fantasy, and everyone lives underground because there’s some sort of techno-magical terror that kills you if you are on the surface when the sun is out. We popcorned a bunch of ideas this suggested: Our communities are in caverns and caves and we eat mushrooms and use magical, portable suns to grow underground crops and stuff. Halflings are irradiated freaks. The purpose of dungeon crawling is, essentially, homesteading. Monsters are leftover killbots from the final war and mutated beasts. Lead takes the place of gold.
To solidify the setting we did something I hadn’t tried before and it worked well. Everyone got four index cards, and we chose an inspirational language for consistency, and wrote down a word, name or phrase on each card. Then we shuffled them up and passed them back out and made a map. They had stuff like MANGU and THE CRUSH and GURLEAN and KHAIDU OLZVOI and THE SILVERED CHAMBERS and RIVER OF ROCK. We took turns filling in details of places and people. Sixteen elements were enough to really breathe life into the world - we have three communities, tenuously connected, all with colorful leaders, and a bandit king who apparently has found a way to survive on the surface. It feels a little lived-in and is just the right amount of detail to start exploring.
It was dirt simple, fast, and really fun.