Bucharest to Sofia by Train
As of current, May 2016, there is a 12:50 train that leaves Bucharest, Romania from the Gara de Nord Station and runs down to Sofia, Bulgaria. This is a long run train that gets you directly from one capital to the other, but is surprisingly not that large of a run; not nearly the large, high speed train that you would expect. It is only a few cars and the train moves very slowly.
Our second class cabin was an old car, no power and eight seats in a small compartment: that is four side by side facing another four side by side. It is a bit cramped and our run was rather full so there was not a lot of free space for people or for luggage.
The train stopped at the Romanian border for exit controls for about two hours. A surprising amount of time for going from one EU country into another and for this being the "exit" side of the border crossing. This takes place long before the train heads over the Danube and only after being on the Bulgarian side for quite some time do you reach Ruse station and Bulgarian entrance border control. But the Bulgarian side took twenty minutes or less, totally painless.
It is great that there is a train between these two countries and travellers will often want to avail themselves of it. We used it for going from Bucharest to Tarnovo. But sadly it is unnecessarily slow with many stops so extensive that everyone gets off of the train to relax outside and the border crossing is just crazy. So what could be a highly efficient and business effective semi-high speed capital to capital run is actually a very slow and somewhat painful experience that is mostly good for casual travellers.
The Bucharest to Sofia Train Crossing the Danube at Ruse, Bulgaria: