The Vennbahn is one of Europe's longest railway track cycling trails, at 125km.  It goes from Aachen (Germany) to Troisvierges (Luxembourg), passing through eastern Belgium along the way.  Since it's a rail trail the grades are very moderate (2%).

The route follows the dike on the Wichita - Valley Center Floodway. Starting at the south end west of the town of Derby and continues north for 31.5 miles along the west side of Wichita and ending northwest of the town of Valley Center. Can be run in either direction.

Admin note: It appears that athletes can chose to run on either side of the dike, or switch sides as they prefer.