Would love to see Giverny,Chartre, and Fountainbleu in 2 days. Is this possible? Going by train. Need to be in Paris by third day to go to London on Eurostar.
Monet's gardens at Giverny are open through 1 November. If you stay in Paris, you can easily take a day trip to Giverny. Take a train to Vernon and then either a bus or taxi to Giverny.
It's possible to visit both Fontainebleau and Chartres in one day, but you'll be extremely rushed and you'll spend a lot of time on the train.
Take the train from Paris Gare de Lyon to Fontainebleau-Avon and the bus from there to the chateau in time to be there when it opens at 09:30.
Getting from Fontainebleau to Chartres will take close to three hours. To get to Chartres you'll need to return to Gare de Lyon. Take Metro line 14 from Gare de Lyon to Bercy, transfer to Metro line 6, and take it to Montparnasse-Bienvenue. Walk to Gare Montparnasse and take a train from there to Chartres.
For a one-day combination trip it would be a better use of your time to visit Versailles and Chartres. Trains go directly between Versailles and Chartres and the trip takes around one hour.