"St. Alexander Nevsky Cathedral (Sofia Bulgaria) "

Built in Neo-Byzantine style, it serves as the cathedral church of the Patriarch of Bulgaria and it is one of the 50 largest Christian church buildings by volume in the world.  St. Alexander Nevsky Cathedral in Sofia occupies an area of 34,100 sq ft and can hold 5,000 people inside. It is among the 10 largest Eastern Orthodox church buildings. It is the largest cathedral in the Balkans. It is believed that up until the year 2000 it was the largest finished Orthodox cathedral.