Not a game yet, but after 4 hours, I have an idea down and the main mechanic implemented.
Funny thing is, I was thinking about this game for the whole week. I was lucky that the theme fits the idea that I want to implement so perfectly.
So the idea is this: a top-down action game. Normal stuff: walls, enemies that shoot you, weapons. I was thinking about something a bit like the air combat of Xenonauts.
But here is the twist: the rooms and dungeons that you fight in are generated randomly, based on your geocoordinates! Is the current level too easy? Go to a nearby coffee shop and see if you can find something better. Need a green key? Somewhere in the way between your house and your supermarket, there may be a dungeon containing it.
Your world and the game world, connected.
Now to make that game happen!