So, a long time ago in a place called Ephesus, there was a really important guy named John. John was one of Jesus' followers and he wrote some really important stuff in something called the Bible, which lots of people still read today.
After John died, the people in Ephesus built a special building called a basilica to remember him and to worship God. This basilica was really big with a dome on top, like a giant upside-down bowl. People would go there to pray and to learn about God and Jesus.
Over time, the basilica got damaged and some parts of it fell down. But people still thought it was really important, so they worked really hard to fix it up again. Now, it's one of the most important places in Ephesus and people from all over the world come to visit and learn about John and Jesus.