Guards wait for the start of former Egyptian President Hosni Mubarak's funeral at Field Marshal Mohammed Hussein Tantawi Mosque east of Cairo, Egypt on February 26, 2020. (Photo by Amr Abdallah Dalsh/Reuters)

Rick Sorenson, owner of the Rio Ramaza Marina, wades in the Sacramento River after securing an old paddlewheel boat on his property as the river makes its way up the levee on Garden Highway in Sacramento, Calif., Monday, January 9, 2017. (Photo by Hector Amezcua/The Sacramento Bee via AP Photo)

Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)

Snow and ice adorn trees in Ovacık district, Turkey on February 20, 2020. The country has been experiencing heavy snowfall this month. (Photo by Sidar Can Eren/Anadolu Agency via Getty Images)

Ice Age – Tibet, China. “This is the Chinese version of the blue ice lake, Pumoungcuo, at an altitude of 5,070 metres (16,600 feet). This lake in Tibet freezes every winter. At night, under the low temperatures of -20C, you can listen to the sound of the ice cracking while capturing the most beautiful winter sky. The blue ice surface and dazzling Orion constellation create a fantasy landscape. I felt so happy to have the stars as my companion on this magical night”. (Photo by Daniel Zafra Portill/Milky Way Photographer of the Year)

Group leader Jane Waithageni Kimaru, 60 years old, shows women how to fight off a potential rapist and escape, during a Taekwondo self-defense class for women in the Korogocho slum of Nairobi, Kenya, Thursday, September 16, 2021. (Photo by Brian Inganga/AP Photo)

A pine marten – one of a few wild mammals doing well in Britain (although they number just 3,700). A fifth of the country’s wild mammals are at high risk of extinction, research shows. (Photo by Maurice Flynn/The Mammal Society)

“The Challenge!” Young boy relishes in a game of tug of war before school. Photo location: Lake Titicaca, Peru. (Photo and caption by Paul Heyman/National Geographic Photo Contest)