Medieval city walls, Ávila, Spain (© Scott Suriano/Getty Images)

Beech trees and wild anemones, Jutland, Denmark (© Nick Brundle Photography/Getty Images)

Newcastle Upon Tyne, England (© Allan Baxter/The Image Bank/Getty Images)

Red lechwe herd crossing marshy plain of Okavango Delta, Botswana (© Ibrahim Suha Derbent/Getty Images)

The Bahamas pictured from the International Space Station (© NASA)

Himeji Castle, Himeji, Hyōgo Prefecture, Japan (© Julian Elliott Photography/Getty Images)

North American beaver in a pond near Wonder Lake, Denali National Park, Alaska, USA (© Paul Souders/Getty Images)

Llansteffan Castle, Carmarthenshire, Wales (© Roy Shakespeare/Loop Images Ltd/Alamy Stock Photo)

Tulip fields, Skagit Valley, Washington, USA (© Claudia Cooper/Getty Images)

Apple trees in spring, Germany (© Smileus/Getty Images)

Aerial view of the Churún Merú waterfall, Venezuela (© AirPano LLC/Amazing Aerial Agency)

North Window with Turret Arch in the distance, Arches National Park, Utah, USA (© Anthony Heflin/Shutterstock)

The Grand National at Aintree Racecourse, England (© Tim Goode/Pool/Getty Images)

Bowling Ball Beach, Mendocino County, California, USA (© Melo Qiao/Getty Images)

The RedBall Project art installation, Centraal Station, Antwerp, Belgium (© Brit Worgan/Getty Images)

Union Square in Lower Manhattan, New York, USA (© Sean Pavone/Getty Images)

American black bear cub in spring, Shenandoah National Park, Virginia, USA (© Scott Suriano/Getty Images)

The Ring of Brodgar, Orkney, Scotland (© Paul Williams - FunkyStock/Getty Images)

Grand Prismatic Spring at sunrise, Yellowstone National Park, Wyoming, USA (© XIN WANG/Getty Images)

London Marathon in London on April 23, 2017 (© CHRIS J RATCLIFFE/Stringer/AFP/Getty Images)

Green sea turtle, San Diego, California, USA (© Ralph Pace/Minden Pictures)

Painting titled 'Saint George and the Dragon' by Paolo Uccello (© Photo 12/Universal Images Group via Getty Images)

White trillium blooming in Ontario, Canada (© Jun Zhang/Getty Images)

Adélie penguins on an iceberg, Antarctica (© Patrick J. Endres/Getty Images)

Kalaloch Tree, aka the tree of life, Kalaloch Beach, Olympic National Park, Washington, USA (© Abbie Warnock-Matthews/Shutterstock)

Leucistic Anna's Hummingbird in the Australia Garden, UCSC Arboretum, Santa Cruz, California, USA (© yhelfman/Getty Images)

El Capitan in Guadalupe Mountains National Park, Texas, USA (© Adam Mowery/Tandem Stills + Motion)

Fujian Tulou complex of historical and cultural heritage buildings in Fujian province, China (© Hongjie Han/Getty Images)

Cheetah, Ndutu Plains, Ngorongoro Conservation Area, Tanzania (© Paul Souders/Getty Images)

Hawaiian lei flower garlands (© Jotika Pun/Shutterstock)