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)

Catholic pilgrim Matilde Madalena de Jesus crawls on a rocky trail carrying a bottle of water on her head during the annual pilgrimage of the dead (Romaria dos Finados), in the city of Juazeiro do Norte, Ceara state, in Brazil October 31, 2016. (Photo by Ueslei Marcelino/Reuters)

Though schools around the globe have different start dates, calendars and traditions, the first day of a new term is an exciting time filled with the prospects of gaining more knowledge, making new friends and building community. Here: Schoolchildren attend their first lesson on Knowledge Day in the town of Turov, Zhytkavichy District, Gomel Region, Belarus on September 1, 2017. Knowledge Day marks the beginning of a new school year in Belarus and is celebrated on September 1. (Photo by Viktor Drachev/TASS via Getty Images)

Performers participate in the Day of the Dead parade on Mexico City's main Reforma Avenue, Saturday, October 28, 2017. Mexico's capital is holding its Day of the Dead parade, an idea actually born out of the imagination of a scriptwriter for the James Bond movie “Spectre”. (Photo by Eduardo Verdugo/AP Photo)

Sumo wrestlers compete during the annual “Honozumo” ceremonial sumo tournament dedicated to the Yasukuni Shrine in Tokyo, Japan, April 18, 2016. (Photo by Yuya Shino/Reuters)

A boy sleds through snow as he enjoys the snow in Bahcesaray district called as planet nine because of roads blocked by snow in winter, in Van province of Turkey on January 22, 2020. (Photo by Ozkan Bilgin/Anadolu Agency via Getty Images)

A robot, developed by start-up firm Asimov Robotics, holds a tray with face masks and sanitizer after the two robots were launched to spread awareness about the coronavirus, in Kochi, India, March 17, 2020. (Photo by Sivaram V/Reuters)

This photo taken late on February 21, 2021 in Milo, near Catania, Sicily, and obtained on February 22, 2021 from Italian news agency Ansa, shows lava flowing along the sides of the southern crater of the Etna volcano as a new eruptive episode of tall lava fountains, known as paroxysm, occurred. (Photo by ANSA/Handout via AFP Photo)