The best way to get around Paris is to use the metro, if you are coming into CGD you can take the train to Gard du Nord then hop onto the metro from there. Metro stations seem to be dense enough that there will be one near to your destination, I didn't see more than a 10 minute walk.
Using the metro fulfilled every Parisian stereotype I had, lovers kissing, gypsies begging, men busking with accordions. The metro was a brilliant way to get around very entertaining.
Just as entertaining for me(though some might not enjoy it) was my pre metro knowledge walk across Paris to reach my hotel. On the map before traveling the walk didn't look every long. I didn't have any frame of reference for Paris, but a similar distance around the Thames in London would be a reasonable walk. Well reasonable to people that like to walk through cities.
With the 30°C heat at 1800 it was probably a little long for a 6Km walk through the city. But the walk was very fortuitous if I had been down in the metro I wouldn't have seen the stunning sights of Paris, large buildings, street gangs, passed out tramps that have pissed them selves and the myriad of cheap suit shops. Shiny silver suits are a steal at 50€.
After a couple of bouts of despair I reached my hotel in once piece, only loosing about 5 kilos in water.