If you are travelling by car the quickest route from the UK will be the Portsmouth to Saint-Malo ferry.
By Ferry: https://www.brittany-ferries.co.uk/
If you want to travel by plane (e.g. if you are coming from places other than the UK) the nearest airports to the Retreat are Rennes and Dinard. Nantes airport operates all year round and is only an extra half hour’s drive. We are roughly four-and-a-half-hours drive from Charles De Gaulle and Orly airports in Paris.
By Plane: https://www.brittanytourism.com/getting-here/getting-to-brittany/by-plane/
Nearest Train Station: Lamballe, 40 minutes drive away.