I guess a common solo ride for me is a18-25mi 50/50 route of paved roads getting out of town, then gravel roads, then paved roads once back in town.
It's some rolling climbing on the paved roads, then a handful of good climbs on gravel as I go in and out of a river valley, and then it's flat for a bit and a steady incline to end.

I do it a good bit since it gets my heart moving with a lot of short steep climbs that are 7-12% grade, it's short enough to be done in 60-80min depending on the exact route and traffic, and half of it is on dead quiet roads with views of a river valley.

Gravel bike is used.