The cheapest way in. Nothing listed is quicker.
Metro M4 then M2 to the Central Railway Station
M4M2 · Metropolitan EAD, the Sofia metroPickup, hours & luggage
Boards at. Sofia Airport metro station, at the eastern end of Terminal 2; the M4 to Serdika, then the M2 from Serdika II towards Obelya
One EUR 0.80 journey: the change at Serdika is inside the metro, and a bank-card tap or a 30-plus ticket allows a transfer within 30 minutes of boarding in any case. The 24-hour and 72-hour passes cover it.
Luggage. Two pieces of hand luggage ride free; each further piece needs its own EUR 0.80 ticket.
Hours. The M4 as on the way in — 05:21 to 23:38 on weekdays, 05:25 to 23:46 at weekends — and the last M4 still meets an M2 north at Serdika II: the last towards Obelya leaves at 00:16 on weekdays and 00:32 at weekends.
