Heres a picture of a painting of a train going from Calais to Paris.
This could be a handy "postcard", with a clue written on the back. Or a fake-clue to throw the players off the main quest. I just like how it looks.
As a side note, I've scheduled this post to appear at just about the time that I'm proposing to my girlfriend on a train. We're on a Dinner Mystery Theatre train (Mt Hood Dinner Mystery Train), enjoying a silly goofy mystery, while having dinner with my sister and step-mother. Wish me luck, eh!