Reims is a city in the Champagne-Ardenne region of France with a compelling cathedral to visit and champagne cellers all around.. It can be seen in a day trip from Paris; it's only 45 minutes away via TGV train.
Reims offers fairly hot summers, good fall weather, and a springtime full of wild flowers.
Perhaps the best temperatures to be had occur around Bastille day in the middle of July, but as usual for wine regions, fall is the best time to go to see and participate in wine harvest festivals.
Summer is a fine time to visit as well. Being close to Germany, you'll find traditional Christmas markets in winter--although it'll be quite cold December through February with a considerable amount of snow most years.
The charts below show the historic high and low temperatures and average monthly rainfall for Reims.