1) Take a Paris–Nantes train from Gare Montparnasse.
2) Head to Nantes bus station, located across from the south exit of Nantes SNCF station.
3) Board the Aleop coach line 13 “Nantes – Fromentine – Noirmoutier”. This line serves several stops on Noirmoutier Island: Barbâtre, La Guérinière, L’Épine, and the Noirmoutier-en-l’Île bus station, its terminus.
Duration: The journey takes about 4 hours 05 minutes from Paris Montparnasse station to Noirmoutier-en-l’Île bus station.