I am planning on taking train down from Slovenia to Greece, and was thinking about adding a stop in Istanbul. But I am not finding much about train routes. Rome2Rio does not list a train route, and has a 17 hour bus ride. the Trainline does not even list Istanbul as a valid destination. There is always flying, but I was hoping to use a rail pass and avoid all the hassle of airport security and overhead compartments.
It would also be cool if there was an overnight train through Sofia, Bulgaria to Istanbul. I thought I saw a YouTube video where a guy goes from Paris to Istanbul but maybe it was Paris to another place in the area.
Also, is it possible to camp on the Greek side, and do day trips into Instanbul? In places like San Diego, CA, you can cross into Mexico without any visa and back.