Xi’an has the most complete ancient city wall in China: a 14-kilometre Ming-dynasty rectangle, 12 metres high and wide enough on top to drive a bus along, ringed by a moat and punctuated by watchtowers. It has guarded the old capital since 1370, on foundations going back to the Tang palace city.
The classic move is to rent a bike on top and ride the full circuit — about 90 unhurried minutes of rooftops, drum towers and drying laundry sliding past below. Go two hours before sunset: you ride the daylight, watch the light turn gold, and roll back into the South Gate as the lanterns come on.