You should go to the Qianmen Subway Station on the south side of the Tiananmen Square. Then take subway Line 2 to DOngzhimen. Get out from Exit B and walk to the east about 350 meters along Dongzhimen Wai Dajie. Turn left at the crossroad then and continus to walk about 300 meters. Then you will see bus 936. Drop off at Huairou Bus Station. Then change to minibus or just take a taxi to Mutianyu then.

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