Domaine National de Saint-Cloud, just outside Paris. It is the ideal spot for nature lovers with 460 hectares of gardens with fountains, sculptures, and majestic perspectives laid out by André Le Nôtre.
Groged du Verdon, France. You could come by rail on the Train de Pignes from Nice to Saint André les Alpes, which is a very lovely journey. Saint André is 25 km / 15.5 miles from Castellas, and you can find taxi contact details and the train timetable here. Once in Castellane you can visit the gorges (during the summer only) either by coach or in a small group by minibus.