Hi Kat,
The
RER B train from CDG Airport to Paris (St Michel-Notre Dame station) will take about 35-40 minutes.
From Notre Dame station you'll need to switch the RER C line to get to
Champ de Mars Tour Eiffel Station. This leg is about 10 minutes.
The tricky part of this transfer is that there will be multiple "directions" possible for the RER C line since it branches into 3 soon after Tour Eiffel station.
Any of the following directions will work:
- Pontoise
- Saint-Quentin-en-Yvelines
- Montigny-Beauchamp
There may be others that I'm not aware of.
An easy way to check whether the next RER C train stops at Champ de Mars Tour Eiffel is to read the overhead stop panels located on the train platform. Here is a
photo of a RER station panel (although it's from a different line, RER A, it will give you an idea of what to look for).
Another option if you'd rather avoid the confusion of the RER C at Notre Dame is to continue on the RER B until Denfert Rochereau, then switching to the Metro Line 6 direction Charles de Gaulle-Etoile and getting off at Bir-Hakeim station. This method will only be about 5 minutes longer.
Best regards,
Ben