The Ming city wall encircles the old city in an irregular line dictated by the terrain — Zhu Yuanzhang's engineers followed ridgelines and river banks rather than imposing a geometric grid. Of the original 35 kilometres, about 25 kilometres survive, with several sections open to walk. The most accessible stretch runs along the eastern edge of the old city near Zhonghua Gate, which is the best-preserved gate complex and itself a remarkable fortification worth an hour of exploration.
The wall varies in height from around 14 to 21 metres and is wide enough on the top for two lanes of cars. Walking the wall gives you a perspective on the city's topography — the hills, the lakes, the river — that street-level travel can't provide. Evening walks along the lit section near Xuanwu Lake are popular with locals.