The Great Wall of China is an absolute must-see when visiting China. The Great Wall winds its way across China covering over 4,000 miles (6,700km). While the latest construction occurred after 1368 during the Ming Dynasty, construction of the Great Wall began over 2,000 years ago. In fact, the Great Wall is actually made up of a number of interconnecting walls spanning China that different dynasties and warlords constructed over the years.
More on the history of the Great Wall from Travel China Guide.
Visiting the Great Wall
The Great Wall of China is easiest visited on a day-trip from Beijing. There are a number of sections easily accessed from Beijing by tour bus, public bus or by hiring transport. The most popular spot for Chinese tour groups is the Badaling Section of the Great Wall, as it is the closest to the center of Beijing City. This means that it is also the most crowded section of the wall and you'll have to fight hoards of bussed-in tourists as well as water and soft-drink touts. If you want to avoid the crowds, but still have a "great" Wall experience, try visiting a different section.
Your guide recommends the Mutianyu Section of the Great Wall. Still an easy day-trip from Beijing, the Mutianyu Section, punctuated by a number of watchtowers, offers amazing views of the Great Wall snaking off into the distance and the surrounding area.

