The group's members carry plastic bags and stroll around to pick up plastic bottles and other junk at the site. As they take the rubbish away, some tourists also help them.

"The natural beauty of Jiankou inspires awe. It is important to preserve its original form. The Great Wall symbolizes our nation. You leave only your footprints here, not rubbish," says Zou, 55, an office worker from Beijing.

He says Jiankou is pretty in all seasons.

But the group cautions people against trying to climb the dangerous parts of the Wall here, such as the watch tower whose name means the "eagle flies face upward". The tower's 4 meters of stone steps have corroded over the years. Last year, the group helped a female American teacher who was trapped in the watch tower.

The local government is now repairing parts of the Wall here.

"To protect the historical site itself is also vital. Sometimes we stop those who try to take away the bricks of the Wall," Zou says.

According to him, the village data show that between 200,000 and 300,000 tourists visit Jiankou every year, including some foreigners. The peak season is summer.

He says about 2,800 people have joined their weekly excursion to Jiankou so far, and each time they've gone with one or two dozen people.

One of them is Yuan Fangchen, who often takes his wife and son to Jiankou with the group.

"Such activities are good for families. My 9-year-old son also learns the importance of environmental protection," says Yuan, 51, a partner in a Beijing law firm.