New Hampshire, US
The Wapack Trail in southern NH is maintained by Friends of the Wapack Trail. There is an out & back race on this 21.4-mile trail, and the race website has information on FKTs (splits in the race). Overall 21.5 (one way) & 43.0 (out & back) mile course records are here: http://ultrasignup.com/results_event.aspx?did=19292
For the duathlon option, run either direction on the point-to-point trail and then ride back to the start by bicycle.
Wapack Duathlon (Bike Leg).gpx693.4 KB
This route on the old FKT site
The one-way (21.5 mile N-S) CR for the Wapack and Back was set in 2017 by Brandon Newbould in 3:01:16.