St. Alexander Nevsky Cathedral (Bulgarian: Храм-паметник “Свети Александър Невски”, Hram-pametnik “Sveti Aleksandar Nevski”) is a Bulgarian Orthodox cathedral in Sofia, the capital of Bulgaria. Built in Neo-Byzantine style, it serves as the cathedral church of the Patriarch of Bulgaria and it is believed to be one of the 50 largest Christian church buildings by volume in the world. It is one of Sofia’s symbols and primary tourist attractions. St. Alexander Nevsky Cathedral in Sofia occupies an area of 3,170 square metres (34,100 sq ft) and can hold 5,000 people inside. It is believed to be among the 10 largest Eastern Orthodox church buildings. It is the largest cathedral in the Balkans. It is believed that until year 2000 it was the largest finished Orthodox cathedral.
Source: Wikipedia
