The easiest way –short of grabbing a cab– to get to the city center from Roissy Charles de Gaulle is to take RERB: follow the signs "Paris par RER" or "Paris par transports en commun" to the train station. Tickets can be bought there from booths and machines (Please note: U.S. credit cards may not work in the vending machines. However, you can also purchase a ticket from a person at the ticket booths, which are near the vending machines). The cost of a one-way ticket ("un billet aller simple") is just over 9 euros. A round-trip ticket ("un aller-retour") is just over 18 euros. The trains run every fifteen minutes or so; the ride takes just under an hour, depending whether you get a direct train or not. Get off at Saint Michel, opposite the fountain, with the Notre Dame cathedral just behind your back. Then walk up the Saint Michel boulevard to the Sorbonne (a 5 to 10mn walk), to your left, behind the "Place de la Sorbonne" square, or to your hotels, located closely in the neighborhood.
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