Can I go to the Mutianyu section of the Great Wall on public transportation from downtown Beijing?

You can take subway line 2, subway line 13, Airport Express Train, or bus line 3, 106, 107, 123, 131, 132, 401, 404, 416, 418, 852, 866, 915, 915 (express), 918, 980, or 980 (express) and get to Dongzhimen first. Then you can take bus line 916 Express or 916 to Huairou North Avenue (Huairou Beidajie) Station. Transfer to bus line h23, h24, h35, or h36 to Mutianyu Roundabout. After arriving, walk about 500 yards to the ticket office of the scenic area. Or, you may take a minivan to the scenic area from Huairou North Avenue at CNY 50-60. Hope helpful!