Hippopotamus mother and calf, South Luangwa National Park, Zambia (© Nature Picture Library/Alamy)

Sassnitz lighthouse on Rügen island, Germany (© Christian Back/eStock)

Marmot peeking out of its burrow (© Scacciamosche/Getty Images)

Grand Canal with Santa Maria della Salute Basilica, Venice, Italy (© RudyBalasko/Getty Images)

Devetashka Cave, Devetaki, Bulgaria (© Jasmine_K/Shutterstock)

Monarch butterflies, Goleta, California (© Craig Rademacher/500px/Getty Images)

Bonsai Rock, Lake Tahoe, Nevada (© Jim Patterson/Tandem Stills + Motion)

St. James Tidal Pool, Cape Town, South Africa (© AmazingAerialAgency/Adobe)

Mount Hood, Oregon (© Inigo Cia/Getty Images)

Pegadung Rock, Lampung, Sumatra, Indonesia (© CK NG/500px/Getty Images)

Giant anteater in the Pantanal, Brazil (© Pedro Ferreira do Amaral/Getty Images)

Chora, Folegandros Island, Cyclades, Greece (© Francesco Riccardo Iacomino/Getty Images)

Volcán Alcedo giant tortoises, Isabela Island, Galápagos, Ecuador (© Tui De Roy/Minden Pictures)

L’arche de Port-Blanc, Saint-Pierre-Quiberon, France (© DaLiu/Getty Images)

Red-crowned crane bowing to his mate in Hokkaido, Japan (© Steve Bloom Images/Alamy)

Female pyrrhuloxia perched on cactus plant, Texas (© outtakes/Getty Images)

The Pragser Wildsee in the Dolomites, South Tyrol, Italy (© Marco Bottigelli/Getty Images)

Sperm whale pod surfacing, Dominica (© Franco Banfi/Minden Pictures)

Aerial view of colourful houses on a headland in Puerto de la Cruz, Tenerife, Spain (© Marco Bottigelli/Getty Images)

Kinder Scout at sunrise, Peak District National Park, England (© john finney photography/Getty Images)

Firefall at Horsetail Fall, Yosemite National Park, California (© Gregory B Cuvelier/Shutterstock)

Bathing boxes at Brighton Beach, Melbourne, Victoria, Australia (© Prasit photo/Getty Images)

Haghartsin Monastery, Dilijan National Park, Armenia (© Alexey Kharitonov/Shutterstock)

Almond trees in full bloom, California (© Jeffrey Lewis/Tandem Stills + Motion)

Mist in the Cowichan Valley on Vancouver Island, British Columbia, Canada (© Kevin Oke/Alamy)

Grand Canyon National Park, Arizona (© Jeremy Janus/Getty Images)

Polar bear cubs playing, Kaktovik, Alaska (© Piriya Photography/Getty Images)

Bamburgh Castle, Northumberland, England (© Blackbeck/Getty Images)

Eurasian red squirrel (© Westend61/Getty Images)