This is Mainz Cathedral, its scientific name is St. Martin's Cathedral, one of the largest and most magnificent cathedrals in Germany, and the cathedral of the Catholic Diocese of Mainz. In fact, the interior decoration of the church has already interpreted that it is a Catholic church. I looked for several places in the market square next to the church, but I couldn't take a complete picture of it. I could only walk to the far end of an alley behind the church, and barely included several towers of the church together (the first photo).