Joan of Arc was burnt at the stake here in 1431, and the memorials range from a lovely statue in the cathedral, through the Tour Jeanne d'Arc, to the church in the market square, the plaque marking the place where the she was burnt, and the inscription, "O Jeanne sans sépulcre et sans portrait, toi qui savais que le tombeau des héros est le coeur des vivants...".

Rouen was badly damaged during the Second World War. You can see for yourself the medieval restoration and the plaque in the catherdral explaining how, if the flying buttresses had been damaged at a certain point the cathedral would have been lost.

Le Gros Horloge is a beautiful astronomical clock near to the cathedral. The Jewish Monument, under the Palais de Justice, may be of interest too.

The Musée des Beaux Arts will perhaps be top of the list of museums to visit in Rouen, followed closely by the Musée de la Céramique and the Musée Le Secq des Tournelles (ironwork museum), amongst others.

You may also like to visit Rouen's botanical gardens, Le Jardin des Plantes. For a quick tour, there's always Le Petit Train and here's another quick reference Rouen site.