International trains provide a large number of routes to Sofia, arriving from such places as Kiev, Istanbul, Vienna, Athens, Thessaloniki, Moscow and other common cities.
The primary trains from Bucharest to Sofia, and back, run twice daily through the border cities of Giurgiu and Ruse. For example, recent trains are scheduled from Bucharest to Sofia in the daytime departing 12:16/arriving 21:33 and a night train departing 20:04/arriving 06:00. From Sofia to Bucharest there are also two trains: a) Sofia 07:45 - Bucharest 17:19 and b) Sofia 19:30 - Bucharest 05:44. One way ticket is around ?25up. Passport control and customs takes place in Giurgiu (RO) and Ruse (BG), approximately mid-trip. Check local train stations for more up to date information.
To Istanbul, the train costs 70 leva (a bus-ticket is just 40 leva), the train departs at around 18:30 (there are 5 buses a day) and arrives at 9:00.
All services are operated by the Bulgarian State Railways , whose schedules are available on the internet in English.
The main railway station (Tsentralna Gara) can be somewhat confusing. Tickets for Lom, Vidin, Ruse, Varna and international cities are sold on the main floor, but for the rest you have to go to the basement. Platforms can be accessed from the main floor down the escalators at the far left corner. Platform numbering is somewhat confusing: Roman numerals indicate the platform number (I to VI), and Arabic numerals (1 to 12) indicate the actual track. Each platform is divided into East and West. Departures and arrivals are indicated on reliable electronic panels, but, beware, they indicate the track number, not the platform! In any case, leaving by train is mostly recommended if you want to travel overnight to destinations on the Black Sea, since trains for Varna and Burgas will leave late in the evening and get you there in the early morning.