You may know about the Badaling section of the Great Wall, which is the only exposure to this ancient wonder for 70% of tourists. It is often overcrowded and much of it is not the original bricks.
The wild parts of the Great Wall, like Jinshanling, Jiankou, and Simatai, are less visited and original. They are the "true" Great Wall, where you can avoid huge crowds of people, and enjoy the original essence of the Great Wall in peace.
Recommended Great Wall Hiking Tours:
2-Day Jiankou Wild Great Wall Camping Tour
3-Day Jiankou to Jinshanling Great Wall Hiking Discovery Tour
5-Day Huangyaguan to Huanghuacheng Great Wall Hiking Tour