The news is basically all good in terms of the best day trips from Paris by train: There’s a wealth of attractions within Ile-de-France, the administrative region that includes Paris and its suburbs — nearly all of these are accessible via the RER or Transilien commuter trains. (And it’s even better if you get a Navigo pass for the week or month — with an all-zone pass, which would include transport to and from Charles de Gaulle airport, you can travel for free on all of these lines.)