France
The Roissey bus takes you in to the centre of Paris behind the Opera. It is not only a cheap form of transport (from a company perspective) but the bus ride helps you get your bearings and leads you into central Paris where you can shop and eat before going to your hotel.
Outside all terminals at CDG airport and at L'Opera
Hopping on and off the bus round the sights of Paris is cheaper and better than taking either the metro (you see more) or taxi (feel safer!).
You can get a ticket for 48 hours, see Trocadero - walk through to the Eiffel Tower and catch it again, get off at Louvre, catch it again, get off at Musee d'Orsay etc.
Or, on your first day, just stay on for the whole round trip to see where you will want to visit later.
Stops all around centre of Paris, pay on the bus.
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