Vietnam’s Son Doong cave, the largest in the world, could hold a 40-story skyscraper inside. The pristine ecosystem has its own river and jungle. Despite its size, Son Doong wasn’t discovered until 1991. It was lost again for nearly two decades and was fully explored for the first time in 2009. (Photo by Jason Speth/HuffPost)

“Cassowaries are large, flightless birds related to emus and (more distantly) to ostriches, rheas, and kiwis”, writes Olivia Judson in the September issue of National Geographic magazine. How large? People-size: Adult males stand well over five foot five and top 110 pounds. Females are even taller, and can weigh more than 160 pounds. Dangerous when roused, they’re shy and peaceable when left alone. But even birds this big and tough are prey to habitat loss. The dense New Guinea and Australia rain forests where they live have dwindled. Today cassowaries might number 1,500 to 2,000. And because they help shape those same forests – by moving seeds from one place to another – “if they vanish”, Judson writes, “the structure of the forest would gradually change” too. (Photo by Christian Ziegler/National Geographic)

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)

Revellers ride during the 54th annual brass band festival in the Serbian village of Guca August 7, 2014. Every year Guca is swamped by thousands of people taking part in the celebration of brass band music. (Photo by Marko Djurica/Reuters)

A Japan fan before their FIFA World Cup Qatar 2022 Group E match between Japan and Costa Rica at Ahmad Bin Ali Stadium on November 27, 2022 in Doha, Qatar. (Photo by Issei Kato/Reuters)

Schoolchildren with face paint resembling tigers take part in a “Kids for Tigers” campaign in Bangalore, India 27 January 2023. The campaign tries to raise awareness on environmental education with outreach programs, workshops, and information on saving tigers in schools and colleges across the country. (Photo by Jagadeesh N.V./EPA/EFE)

Black softshell turtle or Bostami turtle (Nilssonia nigricans), extremely rare and critically endangered species of tortoise is seen in a pond in Chittagong, Bangladesh on March 1, 2022. For decades, the breeding grounds have shrunk and their habitat has been threatened by habitat pollution. (Photo by Mohammad Shajahan/Anadolu Agency via Getty Images)

Turkish police detained dozens of demonstrators participating in an LGBT pride march in Istanbul, Turkey on June 26, 2021. Police fired tear gas, rubber bullets and blocked attempts by protesters to gather in large numbers after a government decision to ban pride events in recent years. (Photo by Diego Cupolo/NurPhoto/Rex Features/Shutterstock)