This is a pleasant 9 km ‘runseeing’ tour of the central and historic parts of Nantes, hitting the key cultural sites, several important churches, a Château, botanical gardens, and Loire River paths. Start at Square Élisa-Mercœur, running by the pretty Miroir d’eau with the castle on your left. Do a loop around the iconic Château des ducs de Bretagne, then head east for 0.5 km along Rue de Richebourg to the Botanical Gardens (Jardin des Plantes). Enjoy a ~1.2 km loop around the lovely gardens, exiting at the north end. LEFT on Rue Gambetta, passing the Fine Art Museum. At the Louis XVI Column, RIGHT on Rue Sully, to get a taste of the Erdre River, doing a loop around the Square Maquis-de-Saffré and the île de Versailles, with its Japanese Gardens. Exit on the west side Erdre River path, heading back south to central Nantes. Use Rue Saint-Léonard to run through the maze-like streets of the historic center. Use the path along Boulevard Jean Monnet to the Loire River, turning RIGHT to head west along the riverside path for 1.3 km, enjoying the water views. At the Memorial to the Abolition of Slavery, RIGHT on Rue Maurice Sibille into the trendy Graslin neighborhood. Run through the Cours Cambronne, then use Rue Crébillon to pass through Place Graslin and Place Royale to the start.
Shorter Option: Eliminating the river path/Graslin section makes this a ~6 km route.
Alternative: Green Line. The City of Nantes has developed a self-guided walking tour, using a Green Line painted on the street. It’s 12 km in length. It’s a nice alternative for a ‘runseeing’ tour of Nantes. More info here.