Sofia Airport is made up of two terminals 1 and 2. It all depends on which company you are traveling with. European flights are generally at Terminal 1.
The advantage of Terminal 2 is the metro. For 1.6Lv (0.8 €) the M2 line gets you to the center of Sofia. It takes around 40 minutes by metro to arrive there.
If you arrive at Terminal 1, you won’t have Métro station. If you want to get the Metro, you need to go at terminal 2. For this, you can take bus 84 or 184 and 3 stops later you will arrive at terminal 2 in about 15 min. If you want to do it by foot, it is doable in 20 minutes walk.
The other solution is the taxi. Between 15 and 20 Lv (7 to 10 € max in the evening to the city center). In 20 min you will arrive at the city center.
The taxis advantage : you save time, especially if you arrive at night and have suitcases.
Please note: taxis and other drivers are plentiful on site waiting for you at the Terminal Arrival. If a taxi accosts you and offers you 20 € for the journey, you can reduce it to 10 € or 7€. Above all, don’t forget to fix the price of the journey with the driver before departure. They generally speak few words of English.
Sometimes, when we arrive after a flight, we can be in a hurry, disturbed or the mood already on holydays. Nevertheless, Remember do not hesitate to negotiate with the driver and clarify the price and the journey before getting in the car, it is the most important to have a stressless journey in car.