The Jardin des Deux Rives, or Two Shores Garden, spans over the Rhine River from Strasbourg, France to Kehl, Germany — so you can run back and forth between two countries. You can start from the Strasbourg side, where the path begins along Rue des Cavaliers. Follow it south to March Nordique in the center of the park. This will take you over the bridge to Germany, where the Rheinpromenade continues along the river. For maximum mileage, head south first until you reach the canal Durchgehede Alterheinzug. Turn north here, pass the first bridge, and continue to the Pont Beatus Rhenanus which will carry you back to the French side of the river. Turn south back into the park to find your starting point. In full, this loop is about 6 km (3.7 miles).
Add-On: For more mileage, the streets in the Kehl neighborhood, around the Marketplatz, out to the Hanauer Museum, are pleasant for running.