I kind of did this already, on my own, a couple months ago. With the intention of creating a mining complex with ore cart tracks built to seemingly logical, rather than haphazard track and tunnel layout. I started with 2 large circles, then gentle arcing "S" shapes.

Not to dissuade a challenge idea, just saying - circles was how I started with this one!

Dhur Naal Mining Complex (in the Finished Maps Forum)