Xi'an (on this list as one of the oldest cities) has a fully preserved (but often refurbished) city wall: https://en.wikipedia.org/wiki/Fortifications_of_Xi%27a

Xi'an (on this list as one of the oldest cities) has a fully preserved (but often refurbished) city wall: https://en.wikipedia.org/wiki/Fortifications_of_Xi%27an https://en.wikipedia.org/wiki/Fortifications_of_Xi%27an It's complete so you can still walk the entire 4 sides of the wall in one hike, or rent a bike and circle the entire city in ~1 hour or so. When you're atop the city wall, there's definitely a sense of being in two different times, both ancient and modern, at the same time as the modern Xi'an skyline makes up the background while you trek on stones that are hundreds (thousands?) of years old.