The train goes beyond Gare du Nord, sometimes subequent stops like Saint-Michel Notre-Dame or Luxembourg are useful for hotels nearby or for changing to metro lines.
They are easily bought there from the machines in the RER station, (€9.50) although when I was there recently some of these were out of order.
QuoteDo we need to book train tickets for the airport to city before we go or are they easily bought when we get there?
They are easily bought there from the machines in the RER station, (€9.50) although when I was there recently some of these were out of order.