Hello.. I'll be in Paris for 4 days. I'll be arriving from South France, specifically Carcassonne. There are two options for me, to either arrive at the Gare de Lyon, or Gare Montparnasse, the latter taking an hour more than the train heading to G. Lyon. I wonder where those train stations are situated, and what's the best way to arrive at my hostel, which will be situated in Monmartre, close to the Saint Coeur, I'm guessing that's North Paris and the Stations are in South Paris...
Any help figuring the local transport system would be great. An idea about the costs would also be appreciated.