I only have a day in Rennes. What's not to miss and can easily be seen on foot?
Whether you are a fan of the Ancient Aliens show or not check out Rennes-le-Chateau.
Despite the similarity of name there is no geographic link between Rennes and Rennes-le-Chateau. Rennes is a city in Eastern Brittany. Rennes-le-Chateau is a small village in the Languedoc in Southern France very close to the Spanish border. They're on opposite sides of the country.
Sorry for the mistake and thanks for the correction Philip.
If you are there on a Saturday, go to the market in Place des Lices--it is the second largest market in France and has an amazing selection. Otherwise, go to the tourist information office and ask for the walking tour brochure. You can see the best part of the city on foot for an hour or two. Also, Parc Tabor is a great place for a stroll--lots of gardens and an aviary. There are some Breton specialty shops, of course, and lots of crepes. Bon vacance.