It is very easy to come to the hotel by train or metro.
From Gare du Nord (Eurostar), metro line 4 to « Saint Germain des Prés »
From Charles de Gaulle airport or Orly airport, RER B to « Chatelet les Halles », and then metro line 4 to « Saint Germain des Prés ».
Here is a link to a map of public transportation you can copy: