Lannion railway

The metre-gauge railway from Lannion to Perros-Guirrec (opened ?1906 -- certainly not August 1616 at any rate! -- closed 1949).
Le petit train des Côtes-du-Nord
See also http://www.railfan.net/lists/rshsdepot-digest/200411/msg00016.html

This is the railway that existed in Leroux's day but had not yet been built when Raoul made his overnight journey from Paris (hence the trip by diligence over the moor from the main-line station at Lannion).