Grab some pamphlets at Office de Tourisme de Vannes. This place will have all the information you need to get the most out of your visit to the region.
You'll be spoiled for sightseeing choice when visiting Vannes. Office de Tourisme de Vannes is a good place to begin here, but there are plenty of other fine attractions to enjoy. Le Chorus Exhibition Centre, Musee de La Cohue, and Vannes Aquarium are not far from the tourist information center and and will cap off your day nicely.