Bulgaria is a member of the European Union and Schengen, so EU/EFTA citizens can enter the country simply with a valid ID or passport. Citizens of many other countries do not require a visa for a short-term (90 days) stay link
The official currency is Bulgarian Lev (BGN), with approximate conversion rate 1 BGN=0.51 EUR. The country is preparing for introducing the euro, so many prices are given both in BGN and EUR.
Currency can be exchanged at local banks or at ATM's, which accept all major cards. Credit cards are widely accepted at shops and restaurants.
If arriving in Sofia by air, you are going to land at Sofia Airport SOF. Most airlines use Terminal 2, except for EasyJet and Wizzair, which typically use (the older and smaller) Terminal 1. There is a free shuttle between the two terminals.
Terminal 2 is just meters away from the Metro. It is also serviced by bus line 84 and by taxi.
To get a taxi from the airport it is best to use the assistance of the operator in the terminal and decline offers of drivers approaching you. The rate should be about 0.50 euro/km during the day, with initial fee of about 1 euro.
If you are arriving in Sofia on August 30 (or earlier), you are probably staying at hotel Kibella for the night. To get there, you can:
Take bus 84 from the airport to "Hotel Pliska" bus stop and walk for about 5-10 min to the hotel
Take a taxi from the airport to the hotel. This is a 5 km ride.
The transportation from Sofia to the Katarino Spa hotel will be by AUBG vans. There are three vans planned for Sunday, August 31:
14:00 leaving from Institute of Mathematics and Informatics (Alvarez-Consul, Cotti, Das, Fasola, Graffeo, Bruzzo, Roubtsov, Mandini)
18:00 leaving from the airport (Biswas, S.Szabo, Sala, Tsanov, Grantcharov, Eper)
22:45 leaving from the airport (Ben-Bassat, Pantev)
For the 18:00 and 22:45 vans: A person with sign "AUBG transportation" will come by in the "Arrivals" zone, near the electronic dashboard
If you would like to get to Katarino by bus:
Get to Sofia Central Bus Station by Metro, bus or cab.
There are buses from Sofia to Razlog leaving at 8:30, 9:45, 11:25, 13:15, 14:00, 16:45. The cost is 10 euro.
From Razlog, take a cab to Katarino (4-5 km ride)