Rouen is known for its Notre Dame cathedral, with its Tour de Beurre (butter tower) The cathedral's gothic façade (completed in the 1500s) was the subject of a series of paintings by Claude Monet.
The Gros Horloge is an astronomical clock dating back to the 16th century, though the movement is considerably older (1389).
Other famous structures include Rouen Castle, whose keep is known as the Tour Jeanne d'Arc, where Joan of Arc was brought in 1431 to be threatened with torture; the Church of Saint Ouen (12th–15th century); the Palais de Justice, ; the Gothic Church of St Maclou (15th century); and the Museum of Fine Arts and Ceramics which contains a splendid collection of faïence and porcelain for which Rouen was renowned during the 16th to 18th centuries. Rouen is also noted for its surviving half-timbered buildings.
There are many museums in Rouen including the Musée des Beaux-Arts de Rouen, an art museum with pictures of well-known painters such as Claude Monet and Géricault. The Jardin des Plantes de Rouen is a notable botanical garden dating to 1840 in its present form.
In the centre of the Place du Vieux Marché (the site of Joan of Arc's pyre) is the modern church of Saint Joan of Arc. This is a large, modern structure which dominates the square. (edited from wikipedia)