The neighborhood surrounding Houhai is known for its nightlife.
It's hard to take the old Beijinger out of Houhai, and you wouldn't want to. This network of three interconnected lakes — Qianhai, Houhai and Xihai — in the center of Beijing is where the laobaixing (common folk) "do their thing," as well as being the entertainment district.
In the winter, men in tiny black briefs "polar bear" (a term used to refer to swimming in icy waters) in the frozen lake, while in summer you'll find them everywhere doing calisthenics on the lakeside still wet from their swim. Houhai is a fabulous area that's great for coffee (you'll find a Starbucks on the southwest bank); food (there are dozens of restaurants from Russian to Hunan, pizza to spring rolls), or just a stroll.
The northern banks are sleepier and all around are a maze of hutong. Take a rickshaw tour and have tea with a family in their siheyuan (courtyard house). On the east bank there's pretty decent jazz at East Shore Live Jazz Café.
Photo by Cygnus78