well, u r in the right place. well, just not long enough.
chateau is sure great, as well as fine art museum, which i believe will hold some guitar concert the night on july 6. the interior is very beautiful and u get monet's gondola in venice, and many flemish masterpieces. u wont see many giant elephants in the world, it's very unique, in chantier naval, across the anne bridge. the cathedral is not really outstanding from outside, but does have some great sculptures, like the face/off(not woo's movie), go check the tomb to the right. Passage Pommeraye is v~~ery beautiful, with some interesting shops. there is a japanese garden at ile de Versailles, but not alike by my japanese friend, anyway, still worth walking or canoeing, also on the wonderful tracks for cycling along erdre river. well, speaking of the gardens, great spots are the one near the train station, north to the nantes fc stadium, east end of ile de nantes, and many others, u may wanna hire a bike (very cheap, many lots in the center) to ride around, especially for ile de nantes, where u may find fake bird nest and other interesting contemporary architectures at east side, warehouse bars, big rings and titan cranes at the west. take the ferry at gare maritime to trentemoult (still public transportation), u get a very quiet village, holy different paces, try some flamed rum crepe near the dock. well, back to right bank, the signs of jules verne can be found everywhere, eg. his musuem (good viewpoint in a small park nearby), feydeau (big lawn for lying, picnic, chatting). and u may find also many signs of super mario. (tips: corner at the front of layayette)
wanna mingle with locals? try the bars at commerce or bouffay, especially those irish ones, john mcbyrne, or Buck Mulligan, u will find everyday is st patrick day. try to dine at La Cigale opposite the graslin theater, very beautiful, u got love it, just have the afternoon dessert and coffee for enjoying the atmosphere and on a shoestring. Best kebab in town is at the back of lafayette, with yellow sign, and the guys looks like mustached Sarkozy. best burger is across the Luis VXI square, walk down the street full of small cafes, until the one never open or with long queue, near subway, best crepe is nearby, too.
july 6,7 are wc semi-final, u may find many crazy guys near passage, graslin, back of feydeau, also in pethe cinema, coz of 3-d live. rue crebillon between place royale and graslin is a good shopping street, for those who do not count their money. be sure to try some brittany cider, muscadet blanc, galette and crepe.