An astonishing sight, given that you're still within the confines of Beijing’s 5th Ring Rd, this double-gated, Ming dynasty walled town was built during the reign of Yongzheng, the last Ming emperor, to counter roving bandits and peasant rebels. It didn't stem the tide, and Yongzheng ended up on the end of a rope in Jingshan Park.
Although few of its original buildings still stand (residents live in newish brick bungalows these days), the 2km-long, 6m-high battle-scarred town walls date from 1640. You can’t walk on the walls, but you can walk around them or inside; enter via the West Gate, which is beside Marco Polo Bridge, or the East Gate, at the other end of the town’s only proper road. On the outside of the southern wall, you can see scars from the Marco Polo Bridge Incident in the form of huge shell holes.
The Museum of the War of Chinese People's Resistance Against Japanese Aggression is inside the Old Town walls.
Take bus 339 from the subway exit.