Tianmen Mountain, China

This mountain measures up to 131 meters in height and runs 60 meters deep. The mountain boasts of a natural cave believed to have formed in 263 AD.
The cave is a natural formation and it's naturally shaped like a door. It is believed to have formed when an old cliff broke and collapsed. Chinese people believe that this formation is unique
The Tianmen Mountain also has a 500-year-old temple called the Tianmenshan temple situated on its top and hence the mountain is a major place of worship for the Chinese. Written as Tien Men Shan in Chinese, the mountain has longer days and shorter nights. The temperature is around 9 to 10 degree centigrade through most of the year. In July 1992, the Heaven Gate Mountain was established as a national park and a potential tourist attraction.

Great Wall of China...

Construction of the Great Wall began in the 7th century BC and continued for hundreds of years. It's the longest fortification ever built, constructed to thwart invasions of Mongolian and Manchu enemies. At its height (well, length), it was more than 3700 miles (6000km) long.