This doodle was great practice in parallel curves. It was really relaxing to work on it.
I'd say this took at least 2 hours or so. I actually finished it some time ago, but I'm just now getting around to uploading it.
I work on these doodles whenever I have random pockets of time. I always like to keep busy, so this is one of my favorite ways to relax and pass the time.
Here's some of my other doodles:
and here's a scanned version of this: