There are many airpline companies that have flights to Sofia, the capital of Bulgaria. There is a flight everyday from almost everywhere. The cheapest and most affordable airlines are: EasyJet, WizzAir, RyanAir, which offer daily flights to Sofia Airport, Terminal 1, Terminal 2.
The venue of the event is 5-10min from the airport by taxi or Metro. There is a direct line of the Metro from Sofia Airport. The metro station next to the event is "Joliot Curie".