I'm taking the train from Istanbul to Bucharest, because despite taking 42 hours, it features several stops in small Turkish and Bulgarian towns that I would otherwise never see in my life, so I'm pumped. However--and this is a big however--there is a 5-hour layover in Sindel, Bulgaria, from 5am to 10am, after spending 6 hours on a regional train. I know I'm going to be hungry and tired, and it looks like there is NOTHING to do in Sindel. Any advice on what to do, or how to get out of there are to a neighboring town? Or am I just going to have to suck it up and camp out in the train station for 5 hours?
Have you checked the Lonely Planet guide book for Bulgaria yet? We certainly found it helpful when we visited Bulgaria the summer.
Why not just rent a car in both countries - that way you can stop and go whenever? I agree with the Lonely Planet suggestion, although the place sounds like a railway junction (and there probably is nothing to do there)
It's going to be a tough ride. Four train changes. You will have almost 15 hours in Plovdiv. Beautiful city. You are right. Sindel is in the middle of nowhere and according all Internet information there is no restaurant there. This is what I would do (if I would ever go for 42 hours train ride with 4 changes of train and without a sleeper car): Buy ticket from Plovdiv all the way to Varna, don't get off in Sindel. Half an hour after Sindel you arrive to Varna. There is plenty to do and eat there. You will have 4 hours time there. Then about half an hour before your scheduled departure from Sindel you will depart from Varna. It's a little backtrack but better than sit 5 hours in the middle of nowhere. You will see Sindel again from the window of your train. You of course stay put and continue to Ruse where you change to the last leg of your journey - to Bucharest.
This is too late to do any good but it brings to mind that on a long train ride we took in Bulgaria a few years back. The locals observed we had brought no food or water and despite the fact they didn't speak English, or know us, and despite the fact that they probably lived right on the edge of poverty; they approached and offered us their food.
Again, while I know its too late, you know you can be driven so that you can stop anywhere or any time (and sleep in hotels) for a few hundred dollars a day. In the event it isn't too late and you are interested, send me a PM.