Dyson sphere program. You just need a little bit of space to be able to retroactively add belts into existing stuff because of the 3d belt placement and logistic drones are cheap, so you can ship loads of stuff with them. It lends itself wonderfully to spaghetti factories, which is my favorite kind of factory.

It’s also absolutely beautiful. You can just stop and watch the glowy cubes flow at night or witness an incredible sunrise over the factory. And that gets better as you progress because, well, you’re building a dyson sphere.