My wife and I did a stopover in Beijing on our way to Australia for our honeymoon and had the best time on our tour with our guide, Cactus. In spite of the cold, we bundled up and saw the Great Wall and the Forbidden City. Cactus not only was incredibly knowledgeable, friendly, and spoke great English, she had great suggestions for interesting photo poses.
Two unexpected bonuses: delicious breakfast at a local hole in the wall (Cactus helped us navigate vegetarian menu options), and a tea ceremony to finish off the day. All around, money well spent and a great time.