Rouen has a pedestrian, street that leads from the the Cathedral to the Vieux Marche, which is where Joan of Arc was burned at the stake, there is a small chruch there along with a market selling fish, veggies etc. About halfway on the street is the Gros Horlage, which is the large, beautiful clock, you can take a tour up in the clock if you have time. There is the Musee De Beau Arts, if you want to check out a museaum. There are a number of bike paths and places to pick up a bike for a few hours if you'd like to bike around town.
The entire town is beautiful, very medievil. If you want a great view of the city I'd recommend taking the number 4 bus up to Mont Saint Aignan, the suburb on the hill, the journey up is lovely, and you can just get off at any point, cross the street and catch the bus back down, restamping your ticket (tickets cost 1.40 and are good for an hour)
I've just come back from spending a semester in Rouen and fell in love with the city.
Chez Pepe was a favorite place to eat, nice, yet casual pl (http://www.chez-pepe.com/presentation.html)