Hi,there
August is the hottest month of the year, so you will definitely have a hot summer Beijing trip. Since you have 6 days, do visit places as many as you can. Great Wall should be always included. Actually, you can spend 1 day at Great Wall and the Ming Tombs, 1 day for Forbidden City and Tiananmen Square, 1 day for Temple of Heaven and Dazhalan Commercial Street, 1 day for Fragrant Hill, Old Summer Palace and Peking University, 1 day for Beihai Park and Shichahai, and 1 day for Summer Palace.