If you are going abroad to Bulgaria either as a tourist or to relocate for a short or long period then you will first want to familiarize your self with how to get around and travel within the country. You have several different options as far as mode of transportation through out the country. However you might not get what you are expecting, especially in regards to the public transit system, which is less than desirable compared to those of most European countries. If public transportation is your travel method of choice when traveling overseas you may want to rethink that when you get to Bulgaria. There has not been much in the way of investments into the public transportation system and it shows. You will find trains and buses to be dirty and run down. The buses are typically in poor conditions and the trains run slow if at all. More often than not trains are cancelled with no warning. The exception to the bad public transportation is Sofia. Trams, trolleys, buses and taxis are available for transport in the city and they are all in great condition. And if you are in a rural area there will be no public transportation at all in most instances. Locals usually just hitch a ride with someone, and offer them some liquids from their best hot travel mug.
The privately owned Hemus Air is the domestic flight operator in the country. Flights typically run between Sofia and Varna all year long and during the summer there are flights between Sofia and Bourgas and between Varna and Bourgas.
The Bulgarian rail system has services to most of the major towns and cities in the country. There are two main lines that link Sofia with Bourgas and Varna. Just remember that travel by train is often less reliable than by bus or plane.
Recently there have been a number of private bus companies set up services in Bulgaria. They offer a reliable, clean and inexpensive method of travel in the country. The buses owned by these private companies are typically much nicer than the public buses owned by the state. You should look for buses run by the company ETAP for the most modern and most comfortable transportation by bus in the country.
The bus station in Sofia is fairly new and is very nice. It is called the Centralna Avtogara and you can get information on times and destinations by looking at the timetables and destinations on their website. There is a button on the page to translate it to English if you do not read Bulgarian.