'I Have a Dream' inscription at the location of Dr. Martin Luther King Jr.'s speech on the steps of the Lincoln Memorial in Washington, DC (© Pgiam/Getty Images)

Polar bear in waters off Svalbard, Norway (© Westend61/Getty Images)

Sơn Đoòng cave in Phong Nha-Kẻ Bàng National Park, Vietnam (© David A Knight/Shutterstock)

Hohenschwangau Castle, Bavaria, Germany (© Mespilia/Shutterstock)

Diamond Beach across from Jökulsárlón, a glacial lagoon in Iceland (© surangaw/Getty Images)

Red-fronted macaws in Omerque, Cochabamba, Bolivia (© Bernard Castelein/Minden Pictures)

Crater Lake in Oregon (© Steve Bloom Images/Alamy)

White Cliffs of Dover, England (© LisaValder/Getty Images)

Foucault pendulum at the Panthéon in Paris, France (© Adolf/Adobe Stock)

Spanish shawl nudibranch on kelp off Santa Catalina Island, Channel Islands, California (© WaterFrame/Alamy)

Huanglong Scenic and Historic Interest Area in Sichuan province, China (© primeimages/Getty Images)

Aït Benhaddou, Atlas Mountains, Morocco (© Alex Cimbal/Shutterstock)

Antique iceboats on the frozen Hudson River near Astor Point in Barrytown, New York (© Mike Segar/REUTERS)

Flamingos in the Eduardo Avaroa Andean Fauna National Reserve in Bolivia (© Art Wolfe/Danita Delimont)

Beach huts covered in snow in Brighton and Hove, England (© Tim Jones/Alamy)

Château de Beynac overlooking the Dordogne Valley in France (© Gareth Kirkland/Alamy)

Glass igloos at the Kakslauttanen Arctic Resort in Saariselkä, Finland (© Lingxiao Xie/Getty Images)

Agoyán waterfall near Baños de Agua Santa, Ecuador (© Laura BC/Getty Images)

Ruins of the ancient Maya city of Calakmul surrounded by jungle in Campeche, Mexico (© Alfredo Matus/Shutterstock)

Gentoo penguins near Danco Island, Antarctica (© David Merron/Getty Images)

Red squirrel in the Highlands of Scotland (© Scotland: The Big Picture/Minden Pictures)

Paddleboarder in Bloody Brook, alongside the Connecticut River in Hanover, New Hampshire (© DEEPOL by plainpicture)

Chu Dang Ya near Pleiku in Gia Lai province, Vietnam (© Quang Ngoc Nguyen/Alamy)

Handicrafts of the Guna people of the Guna Yala archipelago, Panama (© Lars Schneider/Tandem Stills + Motion)

Lightning strikes near Church Rock, New Mexico (© Tim Fitzharris/Minden Pictures)

Heart Reef, part of the Great Barrier Reef off Queensland, Australia (© Peter Adams/Offset by Shutterstock)

Taormina, Sicily, Italy (© Juergen Schonnop/Getty Images)

Arctic wolf family in Canada (© 4FR/Getty Images)

European robin during a winter snowstorm, Peak District National Park, England (© Ben Robson Hull Photography/Getty Images)

Svalbard Global Seed Vault with a glittering facade designed by artist Dyveke Sanne, Svalbard, Norway (© Pal Hermansen/Minden Pictures)

Mittenwalder Hütte in the Bavarian Alps of Germany (© Sebastian Frölich/Offset by Shutterstock)