Children playing on Walled City rooftop in Hong Kong, 1989. The lack of formal governance in the Walled City led to challenges, but it also fostered a unique system of informal social order. (Photo by Greg Girard/The Guardian)

A runner competes in the Great Wall Marathon at the Huangyaguan Great Wall outside Beijing, China, May 18, 2019. (Photo by Thomas Peter/Reuters)

A woman sentenced to starvation death...

An artist shows her hands after working on a wall as part of a campaign to call for coexistence and the renouncement of violence through the painting of walls in Sanaa, Yemen March 15, 2015. (Photo by Mohamed al-Sayaghi/Reuters)

Arcelia Aguilar, a resident of “Hogar Jardin De Los Abuelitos”, receives a hug from her niece Maria Aguilar through “El muro de los Abrazos” (The Wall of Hugs) which is a wall made from plastic sheets to protect against the coronavirus, in San Salvador, El Salvador on September 1, 2020. (Photo by Jose Cabezas/Reuters)

A Chinese tourist visits the Mutianyu Great Wall covered in snow on February 23, 2021 in Beijing, China. Affected by the new coronavirus (COVID-19), the number of visitors to Mutianyu Great Wall in 2020 dropped by about 60%. (Photo by Lintao Zhang/Getty Images)

A stunt rider performs on the wooden wall during a fair in Bogra, Bangladesh, February 10, 2021. (Photo by Xinhua News Agency/Rex Features/Shutterstock)