St. Peter's Cave Church in Antioch
"So Barnabas went to Tarsus to look for Saul, and when he had found him, he brought him to Antioch," we read in Acts 11. "For a whole year they met with the church, and taught a large company of people; and in Antioch the disciples were for the first time called Christians."
Some believe that this cave, on the side of Mount Starius near Antakya (Antioch), Turkey, is where those first Christians gathered. Christian tradition considers the Apostle Peter to be the founder of the Church of Antioch.
The oldest surviving parts of St. Peter's Cave Church date from at least the 4th or 5th century, according to Wikipedia
, which adds, "The tunnel inside which opens to the mountainside is thought to have served the Christians for evacuation of the church in case of sudden raids and attacks. Water which seeps from the nearby rocks was gathered inside to drink and to use for baptism; flow of this water, which visitors drank and collected to give to those who were ill (believing that it was healing and curative), has lessened as a result of recent earthquakes."