Now that you've gotten outside of Paris proper and need a bit of fresh air and green trees, is it natural to take a walk along one of the rivers. The river Marne comes from the east of Paris and merges with the Seine river just outside of Paris. It is 525 km long and large enough that there are both cargo and house boats sailing on it. The river goes through parts of the champagne area and when it reaches the suburbs of Paris it becomes a green space in the middle of a city.
There are walk and bike paths along the entire river through the suburbs, grass and trees, parks and restaurants, sports clubs, boating, locks, bathing, camping and so on. The bridges which crosses the river are often both interesting and historical. The rivers of France still plays a vital role for culture, leisures and business. They are yet important means of transportation through the country and it's interesting to see a large barge sail past heavily loaded with cargo. The house boats are fascinating and a real alternative to the usually steep rents in the Ile-de-France region.
The river banks become places of gatherings for the locals during the summer. Young people date, elder plays petangue, mothers take their children for a walk, families meet to picnics, the healthy exercise and there's always life and a good chance to see typical French life. You can easily find a romantic spot for an hour of relaxation before you again face the challenges of exploring Paris.
Outside of the suburbs the river becomes the centre for the towns, often with a strong historical touch and plenty of charm and soul. It is not hard to find old city walls, historical bridges, monasteries, old narrow cobblestone streets, warehouses and so on. It is easy to see that the river played an important role throughout all history.