How do you get from the Eiffel tower to CDG airport by train?

To get from the Eiffel tower to CDG airport by train, follow these steps:

1. Take the RER C train from the Champs de Mars - Tour Eiffel station to the Saint-Michel Notre-Dame station.

2. Change to the RER B train heading towards the Charles-de-Gaulle Airport (CDG).

3. Get off at the CDG Airport station and follow the signs to the airport terminals.

The journey time from the Eiffel Tower to CDG airport by train is approximately 1 hour and 15 minutes.