I have a stockpile of ideas after I finish the Lavender Remake, as I have a whole summer to finally have fun.
One of these ideas... a terrain map which is mostly indoors. It would be a low-gravity map within a mostly-glass structure, with domes and transport tubes and ship docks... the terrain would pretty much be for realism (preferably Mars... or would the Moon's surface look cooler?). There would be other structures you walk through, such as terraforming stations outdoors, refineries underground, and other miscellaneous things you would find in an arcology-type building.
I'm thinking perhaps in the style of D-Man's recent glass-based maps (sky-wfa), and it would kinda be like those hamster playgrounds, only how it would really be constructed in real life when we eventually colonize other planets for humans to walk through in the future.
Good idea, bad idea?