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)

Young Slovaks dressed in traditional costumes throw a bucket of water at a girl as part of Easter celebrations in the village of Trencianska Tepla, Slovakia, April 9, 2012. Slovakia's men splash women with water to symbolize youth, strength and beauty for the upcoming spring season. (Photo by Samuel Kubani/AFP)

A hummingbird feeds on the nectar from a Mimosa tree in Saugus, Massachusetts on July 30, 2020. (Photo by Joseph Prezioso/ZUMA Wire/Rex Features/Shutterstock)

A man runs on a small road in the outskirts of Frankfurt, Germany, before sunrise on Tuesday, September 1, 2020. (Photo by Michael Probst/AP Photo)

People look at a dead pilot whale on a beach in Panadura on November 3, 2020. Rescuers and volunteers were racing since November 2 to save about 100 pilot whales stranded on Sri Lanka's western coast in the island nation's biggest-ever mass beaching. (Photo by Lakruwan Wanniarachchi/AFP Photo)

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)

Fireworks illuminate the Ampera Bridge during a New Year's Eve celebrations in Palembang, Indonesia on January 1, 2020. (Photo by Muhammad Tohir/Sijori Images via ZUMA Wire/Rex Features/Shutterstoc)

A worker sprays disinfectant as sanitization operations against Coronavirus are carried out in the museum hosted by the Maschio Angioino medieval castle, in Naples, Italy, Tuesday, March 10, 2020. (Photo by Alessandro Pone/LaPresse via AP Photo)