Tourists visit the Badaling Great Wall in Beijing, capital of China, June 10, 2018. The Badaling Great Wall received more than 20,000 visitors per day recently. (Xinhua/Li Xin)

Tourists visit the Badaling Great Wall in Beijing, capital of China, June 10, 2018. The Badaling Great Wall received more than 20,000 visitors per day recently. (Xinhua/Li Xin)

Tourists visit the Badaling Great Wall in Beijing, capital of China, June 10, 2018. The Badaling Great Wall received more than 20,000 visitors per day recently. (Xinhua/Li Xin)

Tourists visit the Badaling Great Wall in Beijing, capital of China, June 10, 2018. The Badaling Great Wall received more than 20,000 visitors per day recently. (Xinhua/Li Xin)

Tourists visit the Badaling Great Wall in Beijing, capital of China, June 10, 2018. The Badaling Great Wall received more than 20,000 visitors per day recently. (Xinhua/Li Xin)