What is the best way to get from CDG to the Gare de Lyon? Is there any way to do it without having to transfer trains?
You have to transfer.
There's a zillion ways, but the least amount of walking on the change is to make it at Chatelet/Les Halles where you switch from RER B to RER A.
Air France bus #4 goes directly between CDG and Gare de Lyon. Buses run every 30 minutes, the trip takes around an hour (more if traffic is heavy), and the fare is 16.50 EUR. These are highway buses so your bags go in the luggage bay.
Thanks, guys. Good info.