The means of travelling around the city really depends on what you came for. If you've come to see the monuments, I suggest you simply walk around the downtown area. Distances are not that big. When you're using a taxi, I suggest you open your eyes. Pick the 'OK Supertrans' company, any person living in Sofia will tell you that they're one of the few that don't try to rip you off. Concerning the city transport, bus number 84 runs from the airport to downtown. If you choose to travel using the public transport, remember that you must punch a ticket for every piece of luggage larger than 60X40 cm. I've seen people get fined because they didn't know that. What you see on the picture is light traffic. I should make a picture of rush hour on a Friday...