I think it’s fair to say most routes in Zwift are automatic loops, an exception that spring’s to mind is Climber’s Gambit.
My goto for a bit of self punishment is New York’s Grand Central “Grand Central Circuit” Route Details (New York) | Zwift Insider , because it’s by far the closest resemblance to my rides in the UK South Downs hills between spring and autumn (up and down 250-600 foot hills). In a way, Grand Central reminds me of “<3 Beacon Hill” <3 Beacon Hill | Strava Ride Segment in Southampton, United Kingdom , a nasty little circuit of pain.