The Val de Seine leisure center is located in the Yvelines, 1h15 from the center of Paris.
There are many leisure bases in Ile-de-France (Saint-Quentin-en-Yvelines, Cergy-Pontoise...). The base of the Val de Seine is located west of Paris, in Verneuil-sur-Seine to be precise, it is only accessible by car. There is a lake for swimming and you can also walk along the Seine. The entrance is free during the low season but from the weekends in May you have to pay 4,60 euros per person. The environment around the base is quite nice, there is even an airfield right next to it. The walk around the base and along the Seine is far from being exceptional. To be recommended if you are in the area and if you want to swim in summer.