Originally Posted by Hypno Toad

For me, it's the Dakota Trail, it's 50+ miles (out and back) with a total of ~615 ft of climbing, or 12 ft/mile. The Dakota is a paved rail-trail running west of Minneapolis. https://www.strava.com/activities/315912883 I've liked it for constant effort rides, in addition to being flat, there are limited road crossings on the west end of this route.