US Army nurses arrive in Greenock, Scotland, 1944 (© Stocktrek Images, Inc/Alamy)

Alpine marmots, Hohe Tauern National Park, Austria (© Raimund Linke/Getty Images)

Emerald Bay and Fannette Island, Lake Tahoe, California (© Bill Stevenson/Cavan Images)

Salt evaporation ponds on the island of Gozo, Malta (© Marius Roman/Getty Images)

Ra Gusela peak at Giau Pass, near Cortina d'Ampezzo, Italy (© Tomasz Podolski/Getty Images)

Salar de Uyuni salt flats in Bolivia (© Abstract Aerial Art/Getty Images)

Corfu at night, Greece (© whitewizzard/Getty Images)

Amur leopard cat, Russia (© Valeriy Maleev/naturepl.com)

Islets of Es Vedrà and Es Vedranell, Ibiza, Spain (© L. Apolli/Getty Images)

Salt flats in Badwater Basin, Death Valley National Park, California (© Jim Patterson/TANDEM Stills + Motion)

Blue-footed booby, Galápagos Islands, Ecuador (© Karine Aigner/TANDEM Stills + Motion)

Third Thai-Lao Friendship Bridge connecting Laos and Thailand (© chaiyut samsuk/Getty Images)

Bleeding hearts (© Dorene Hookey/Cavan Images)

Humpback whales in Monterey Bay, California (© Kiliii Fish/Cavan Images)

Lincoln Memorial, Washington, DC (© Westend61/Getty Images)

Red lanterns celebrating Chinese New Year (© Gins Wang/Getty Images)

Przewalski's horses (© Nemyrivskyi Viacheslav/Getty Images)

The Dragon's Eye rock formation at Uttakleiv Beach, Norway (© reisegraf/Getty Images)

Horsetail Fall in Yosemite National Park, California (© Jorge Villalba/Getty Images)

Red fox standing in snowfall, Grand Teton National Park, Wyoming (© Radomir Jakubowski/naturepl.com)

The hill of Mam Tor, Derbyshire, England (© john finney photography/Getty Images)

Great white egret, Upper Bavaria, Germany (© Konrad Wothe/naturepl.com)

Water lilies at Grand Cenote, Tulum, Mexico (© Christian Vizl/Tandem Stills + Motion)

Ice cave in the Mendenhall Glacier, Alaska (© Designpics/Adobe Stock)

Grand Canyon and the Colorado River, Arizona (© Matt Anderson Photography/Getty Images)

Polar bear cub walking across pack ice, Arctic National Wildlife Refuge, Alaska (© Steven Kazlowski/naturepl.com)

Olo'upena Falls, island of Moloka'i, Hawaii (© Andrew Aylett/Getty Images)