The medieval ramparts of Vannes form an almost complete circuit around the old town, and walking the full length takes less than half an hour. The walls are best approached from the south side, where the fortifications drop down to the Jardins de la Garenne — formal gardens laid out along the river Marle in the seventeenth century, with the towers reflected in the water below.
You can walk along the top of part of the walls and through several of the gate towers. The Porte Saint-Vincent on the south-west corner is the grandest: a seventeenth-century baroque gateway with an ornate niche above the arch. The ramparts and gardens together make Vannes one of the most photogenic towns in Brittany, and they're free and open at all hours.