Hi
Just a heads up about the music festival in Paris (and all over) on June 21st night. It is light til about 11 pm. Last year we found ourselves walking for miles at the end of an exhausting week and day of traveling because the buses were not running their normal schedule. Subways were overstuffed with young black dressed Frenchies.
The route down St Germaine was closed. The driver wouldn't let us on the bus. The street was filled with people shoulder to shoulder and live music was everywhere. Could be a lot of fun if you have the energy. Long lines for food and expensive street vendors set up.
As tired as we were, with an 8 year old we suffered through the long long walk thinking the hotel was just ahead. Long lines for food and expensive street vendors.
So plan ahead and see if the routes you need will be closed.