You want a Great Wall hiking? Well, I can give you a good itinerary for reference:
Beijing - Badaling - Huanghuacheng - Jiankou - Mutianyu - Beijing
To go to Badaling, you can take the Bus No.919 at Deshengmen Gate. Also you can find the special buses at Tiananmen Square. It will take you about one hour to get to the destination. After arriving at Badaling, going on walking eastward, you will pass Huanghuacheng, Jiankou and Mutianyu.

The buses of ‘Chengde – Beijing’ pass near Mutianyu. You may take it to go back to Beijing.