I live right on the Greenway which is about 8 miles end to end, so most often I use it, or part of it, for the out and back portion, before a "loop" on the roads. I have a few favorite loops, that I can stack and merge depending on how good it feels at the moment.

Not always though. In the summer I sometimes like to pick a route from Strava heat-maps almost at random, and just go. There's probably a dozen that I haven't got to yet.