To add to what Paul/Matt posted, the Oil Creek and Titusville RR has the only working Railway Post Office (their claim, not mine) in the U.S. Last time I was there, one of the souvenirs I bought was a OC&TRR postcard which I mailed to myself from the train. I wrote to myself "I wish I was here."
While in the area, for history buffs it is worth it to visit Drake's Well. I would do this after the train ride.
Andy