Wikipedia
Jiankou is a section of the Great Wall of China. This section is a photographic hotspot due to its unique style, steep mountains and beautiful scenery. 'Jiankou', is translated as 'Arrow Nock' in English, for the shape of the collapsed ridge opening is reminiscent of an arrow nock.
The Jiankou section of the Great Wall of China is located in the Huairou District 73 km north of Beijing. The Jiankou section of the Great Wall of China is located between the Mutianyu - ten kilometers to the east - and the Moshikou sections of the Great Wall of China. The Jiankou section of the wall was constructed in 1368 during the period of the Ming Dynasty. It is made of large light colored rocks which can be seen from a great distance.
The Jiankou section has never been restored since its construction, with some sections having fallen into disrepair. This, along with its location along a mountain ridge bordered by jagged cliffs and steep drop-offs, makes this section potentially dangerous to climb, while at the same time a popular place for adventurous and experienced hikers and photographers. The section is more easily reached from villages like Xizhazi and Jiushuikeng at the north side of the wall, locally known as Hou Jiankou , than from the south, called Qian Jiankou . The climb from the north goes up just over 100 meters in about a one kilometer hike, whereas from the south the climb is about 450 meters up over a horizontal distance of also one kilometer.
There are many scenic sites along the Jiankou Great Wall of China, one of which is the watch tower known as "The Eagle Flies Facing Upward" . This tower appears extremely high as it was built on a mountain which forms the highest section of the Jiankou Great Wall. The eagles can only do so facing upwards before reaching the top of the tower when they pass through here. The "Sky Stairs" is another famous scenic spot with a precipitous stair whose angle of elevation is 70 to 80 degrees. The stairs are so narrow that it is barely possible to obtain a foothold.
Other scenic areas include the Beijing Knot (the meeting point for three walls coming from different directions), the Nine-Eye Tower (a watchtower with three layers, and nine holes which look like nine eyes on each side), the Zhengbei Tower (a good place to watch the sunrise and the sunset), the Cloud Stairs (a section of the Jiankou Great Wall which rises like a staircase into the white clouds), and many other watch towers.
Because of its connection with Mutianyu, along with its relative sparseness in visitors, the Jiankou-Mutianyu trail is one of the most popular Great Wall hikes today.