Bulgaria night trains

A little over a year ago we did somewhat the same thing you want to do. We took an overnight train from the Istanbul station to Stara Zagora, Bulgaria. It was fifteen hours with several stops including one on each side of the Turkey-Bulgaria border. I think that is the closest you can get to Bucharest on one train with no transfers. That was a terrible ride. We chose third class, a big, big mistake. The car was ancient, window up or window down ventilation, squat toilets without water or paper on each end of the car. Just bad. If you take this route go first or second class. The train leaves in the evening so you can have dinner at the station's Orient Express restaurant. We spent three days in Stara Zagora, an interesting small city, before resuming the train trip to Bucuresti. That is a straight shot with stops but at least you stay on the same train. We can give details on staying in Stara Zagora if you wish. Also we can go into detail about the train station, and buying tickets in Istanbul and Stara Zagora.

I answered your question under To the East.

Monte, I have a feeling your sharing your experience here is going to be very helpful to Charles!!! What an experience that must have been. Yikes!!