 It is navigable by ocean-going vessels as far as Rouen, from the sea.Over 60 percent of its length, as far as Burgundy, is negotiable by commercial riverboats, and nearly its whole length is available for recreational boating; excursion boats offer sightseeing tours of the river banks in Paris, lined with top monuments including the cathedral of Notre-Dame, the Eiffel Tower, the Louvre Museum and Musée d'Orsay.There are 37 bridges within Paris and dozens more spanning the river outside the city.