3 year old Giant mountain bike for sale for 700 kuai. New gears, new handle bars, new-ish brakes, and new-ish seat. Great condition, just needs a new home. I am about 5'5" and it fits me well. It is a bit dirty (to help it blend with other bikes so as not to get stolen), but there is nothing wrong with the bike. Just dusty. Comes with a rack, fenders, and a white lock (one of those stretchy ones).
I live near Jianguomen, and can meet you either at that subway station (exit A) or at Galaxy Soho (chaoyangmen exit G).