I don't really have one, there are 4 standard 2hr routes (each with variations to keep things more interesting, but all timing out at about 2 hr) that I take from my driveway. One of those routes can sometimes have some traffic, so maybe not that one on a holiday get-away Friday. Then another set of 3 hr, 4 hr and up routes (normally incorporating some portion of the 2 hr routes), up to 100 mi. If I'm riding the tandem with my wife, I can adjust the routes to a slightly lower speed (this is becoming less of a necessity as my wife's cycling fitness improves).

I'm spoiled, there are a lot of nice cycling roads near me.