My preferred means for getting around France is by train. The train system in France is very efficient with trains running throughout the day on most lines. The one downside is the occasional strike. Paris acts as the hub, with just about all-major lines connecting through it. Tickets can be bought on-line at Voyages Sncf UK or at most train stations in France. Most but not all tickets are cheaper the earlier you buy them.
The TGV (Train à Grande Vitesse) train travels at up to 180 miles an hour, making Bordeaux only three hours from Paris. The vast majority of lines in France do not use the TGV; check ahead if the type of train you would like to travel on is TGV.
TGV trains are quiet and you don't feel any bumps. Just about all have a dinning car, but I would suggest you bring your own meal, eating on a TGV can be expensive. TGV seating is similar to airplanes but with more legroom, you have a tray, overhead compartment and seating is four across with a passage in the middle.
The main TGV lines are Paris - Marseille, Paris - Bordeaux, Paris - Lille, Paris - Lyon and Paris - Nantes. There is also a TGV train that serves CDG airport and 'low cost' routes with iDTGV.
If you're going from city to city then taking the train is the best way to travel. Costs are not that high and time wise the train can be better than a car. Trains are normally economical for parties of four or under.
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