The Great Wall
The best known historic structure in China is by far The Great Wall, built over a period of 2,000 years, although most of what is seen today dates from the Ming Dynasty. At least 20 Chinese States and Dynasties contributed to the construction of the wall folllowing many different routes. The first sections of the wall were built by the Kingdom of Qi in 500 BC. When China was finally unified in 221 BC, under the Qin Dynasty, the existing sections of wall were connected and extended, first rammed earth and later stone and brick were used in construction. The early Ming emperors almost entirely rebuilt the wall, extending it to an estimated total length of over 3,000 miles from Shanhaiguan to Jiayuguan. Several sections of the wall are open to visitors at Badaling, Mutianyu, Simatai, Huanghua, and Jinshanling, near Beijing.
Section of The Great Wall above Juyong Pass
Another section of the Wall above Juyong Pass
More Wall above Juyong Pass
A portion of the fortress in Juyong Pass located  50+ kilometers to the northwest from downtown Beijing 
Starting the climb up the Wall from the fortress
It's a long steep climb to the top of the Wall above the Pass.
Looking down at the Fortress from just below the second watch tower
Looking down from the third watch tower
Looking up to the fourth watch tower
Looking down from the sixth watch tower, and still not at the top
Looking across to the other side of the Pass
Pagoda along the Wall above the Pass
Near the summit above the Pass
Heading back down after reaching the summit above the Pass
Back down at the fortress after a long hard climb. When we reached the top we found that we were the only ones there, it seems everyone else gave out before they got that far.
Part of the fortress in Juyong Pass