The best maintained section of the wall surrounds Xuanwu Lake Park. The lake, which was once used for naval exercises during the Song dynasty, has five tiny islands connected by bridges and graced with elegant teahouses, restaurants, gardens, pavilions, an open-air theater and even a zoo. Although the main entrance to the park is on Zhongyang Lu, I like to go in through Jiefang Men (Liberation Gate) as it is less touristy. Inside, you'll find old men fishing and people picnicking, paddleboating or riding tandem bicycles. (Bicycles and paddleboats can be rented for just more than a dollar an hour per person at concessions located throughout the park.)
Enter through Jiefang Men, turn right and you will soon find a staircase that leads you through a hole in the city wall. It then takes you through a bizarre dormitory-like office built inside the wall and eventually up and back out again. The top of the wall makes for a comfortable, even exhilarating walk, about half an hour in either direction. The path, which was rebuilt in the 1980s, is wide and solid, and the view is expansive: the shimmering lake to the north, and Purple Mountain to the east, where Emperor Zhu's tomb still stands.