This is one of the more interesting entrances to the old city. It curves inside the wall and is more like a tunnel. You can see the curve in the middle photo. The third photo shows the exit into the city, but it also gives a feel of how dark it would have been without lights.
Most of the old German cities have only a small section of their old wall remaining, due to the horrific bombing of World War II. Some tore down remaining walls because the openings were too small to allow fire trucks into the old section, or they felt they needed to widen the streets for modern traffic. I'm so glad that Nürnberg did not do this; being enclosed within a city wall is the only way you can get a feel for the size both of the city and the thickness and height of the wall. It emphasizes the fact that everything is within walking distance, and helps give a feel to life "back then."
I was awed to think that both Albrecht Dürer and Maria Sylabilla Merian walked this town and through this entrance.