Its not vatican
According to the Catholic Encyclopedia the Cenacle (the site of the Last Supper) in Jerusalem was the "first Christian church" but Dura-Europos church in Syria is the oldest surviving church building in the world.
Who or what is Rosemary, the stone image carved behind the choir of the 13th-14th century St. Mary's Church in Lübeck, third largest church in Germany?
During the Great, or Western, Schism from 1378, there were two or more Popes recognised in the Catholic Church. Who was elected in 1417 and eventually recognised by the majority as the single Pope?
Which of these is the eastern part of a non-collegiate Christian church, sometimes known as the choir, usually separated from the nave by a screen or railing?