Saint-Malo has a good bus system, with the main terminals located at the train station and just outside the wallsSt Vincent. Get a booklet with maps and times from any bus driver. A one and a half hour ticket costs €1.15. Unfortunately there are no bus services late in the evening.
The walled city is easily covered on foot, but you can also opt for a dinky "Tourist Train" that takes you and your wallet for a ride €5.50.
