As an amalgamation of several units, the Great Wall of China has many access points. You can visit the attraction from any one of these points in Beijing. Mutianyu is a section of the Great wall that is restored and houses watchtowers making it a nice spot for photos; it is about 90 minutes from Beijing. Badaling makes it easy to combine a visit to the Ming Tombs. This section of the wall is very touristy so expect large crowds; it is further from Beijing hotels, about 2 hours away. Simatic is a good place to visit after dark as the entire section is lit up. Jiankou is more of an adventure as this section is the least restored and has some challenging areas; it is about 3 hours away from the capital.