The Door of Paradise is a major "attraction" in the "attraction area" of Florence's Cathedral of Santa Maria del Fiore. Hahaha, you didn't expect it, right? It's a door of the baptistery attached to the church.
Although it looks magnificent, it's actually not very large. It's just a double door of normal size. It's mainly famous for the 8 murals on this door, which tell 8 stories.
Just look at it from the outside, and don't queue or buy tickets. So it's a tourist attraction that many tour groups will go to, and the tour guide will take you there to explain.