To transport yourself and your bike from the airport to the starting point of your tour, and then back again to the airport upon conclusion of your tour, you'll most likely travel on the French National Railway (abbreviated in French as SNCF.) To transport your bike on some trains in France -- specifically, the TGV high-speed express trains -- you'll need a canvas, bicycle-carrying bag referred to as an "housse" in French. The SNCF will not allow you to transport your bike on a TGV train without such a bag.
Bicycle-carrying bags are available from a number of manufacturers, including Brulé Mountain Gear. Brulé's model requires no disassembly of the bike, only removal of the wheels. We don't, however, recommend carrying your bike in this bag for any distance (it's awkward and clumsy). Instead, ride your bike to the train station (give yourself extra time); then before boarding, place your bike into its carrying bag as close to the platform from which your train is departing as possible. When the train arrives at the platform and comes to a complete stop, carry your bike onto the same car in which you will be sitting. (Note: seating is always reserved on TGV trains.) Place your bike in the oversized luggage storage area at the entrance of the car. If you have any questions or concerns, stay with your bike until you have an opportunity to speak with a conductor.
On regional and other non-TGV trains that permit bikes, you won't need a bicycle- carrying bag. Instead, you'll stow your bike in the train's baggage car. Before boarding, we highly recommend asking station personnel to specify the baggage car on which you are to place your bike and position yourself on the platform accordingly. You are responsible for both loading and unloading your bike. Similarly, you should prepare in advance for your bicycle's retrieval from the baggage car as you near your destination. As the train nears your stop, walk through the train to the exit nearest the baggage car. When the train stops make a beeline to it, as you will have limited time to unload your bike. French trains always keep to their schedules.