This the only train service going to and from CDG airports.
It will arrive in terminal 2, underneath the airport and is directly under the main lobby.
Tickets are not that expensive, but this train goes from CDG to Saint Remy. In between, Gare De Nord and a few other stations picks up tons of people.
If you are transferring with the Metro, the main spots would be Gare De Nord and Chatelet Les Halles.
While it is not the cleanest of the trains, I was surprised that we were often delayed, which is why I made it a star less. We were on a time frame and stopping for 10 minutes here and there was annoying.
Be mindful of the schedule if you are trying to do last minute things.
from the website: http://easycdg.com/rer-charles-de-gaulle-airport-cdg-to-paris-by-train/
Trains run every day, including public holidays, with departures every 6 to 15 minutes :
* Charles de Gaulle airport From 04:50 to 23:50
* Paris-Gare du Nord From 04:53 to 00:15
Average journey time between Paris-Gare du Nord and CDG airport is 35 minutes. read more