It is 10pm on a Thursday, and the couture shops of ultra-fashionable Sanlitun neighbourhood in downtown Beijing have wound down, but one area remains a hive of activity.

Just a year ago, that would have been the raucous bars of what the locals called Zhangjie - or dirty bar street - but today that space has been cleaned up, replaced by Sanlian Taofen bookstore, a 24-hour paean to the physical book.