Can't find China Post Office, can you tell me where is the nearest?

I'm in Beijing, near Wangfujing station and the Beijing Hotel. I want to send a parcel by surfacace but can't find a China Post Office. Google maps is telling me there's on in a building with a McDonalds but I can't see it and another in the Grand Hotel but ca'n't see it from the outside. I've only found a EMS company but I'm not sure if they send surface parcels, but only Express. And I want the cheappest way. Thank you veeeerry much.