We visited Annecy for a day while staying in Grenoble. Very easy access by train (45 minutes with no train change, or slightly over 1 hour with a change). No need to rent a car. All the shops, the lake and park are within walking distance of the train station. We rented a boat and rode out into the lake for an hour or so. Really liked this place. Recommend Tuesday morning because it is market day. We bought cheese, bread, sausage, fruit and drinks and had a picnic in the park. Market closes at noon. If you do this, be sure to bring a plastic knife to cut things.
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