Chestnut-mandibled toucan in nest cavity, Costa Rica (© Greg Basco/Minden Pictures)

Polar bears in Torngat Mountains National Park, Canada (© Cavan Images/Offset by Shutterstock)

Jal Mahaal water palace at lake Man Sagar, Jaipur (© Amit kg/Shutterstock)

Caribou swimming across Alaska's Kobuk River during fall migration (© Michio Hoshino/Minden Pictures)

Albarracín, Spain (© Domingo Leiva/Getty Images)

West Indian manatees in Three Sisters Springs, Crystal River National Wildlife Refuge, Florida, USA (© Norbert Probst/Getty Images)

Chestnuts inside their husks (© Kai Keisuke/Shutterstock)

Derwent Island on Derwentwater in the Lake District National Park, Cumbria, England (© Chris Warren/eStock Photo)

The hills of Barolo vineyards in Piedmont, Italy (© Marco Arduino/eStock Photo)

Badlands National Park, South Dakota, USA (© Dennis Frates/Alamy)

Mist surrounding a forest in Munnar, Kerala (© Ahammed Riswan/EyeEm/Getty Images)

Connery Pond and Whiteface Mountain in New York state, USA (© Henk Meijer/Alamy)

Ravens in a snowstorm near Kuhmo, Finland (© Frans Lemmens/Alamy)

Ravens in a snowstorm near Kuhmo, Finland (© Frans Lemmens/Alamy)

Lupins on the shores of Lake Tekapo in New Zealand (© Stanislav Kachyna/Shutterstock)

The interior of the Abu Simbel Great Temple in Egypt (© George Steinmetz/Getty Images)

Mixed forest, Füssen, Bavaria, Germany (© Erich Kuchling/DEEPOL by plainpicture)

Inukshuk silhouetted against the Northern Lights in Barren Lands, Northwest Territories, Canada (© Mark Duffy/Alamy)

Aerial view of the Aiguille du Midi in the Mont Blanc massif, France (© Amazing Aerial Agency/Offset by Shutterstock)

An Indian leopard on the prowl (© Colin Langford/Getty Images)

Common cranes in the Drömling wetland in Germany (© Mike Friedrichs/Getty Images)

Common cranes in the Drömling wetland, Germany (© Mike Friedrichs/Getty Images)

Huge waves crashing on rocks along Asilomar State Beach, Pacific Grove, California, USA (© Sheila Haddad/Danita Delimont)

Huge waves crashing on rocks along Asilomar State Beach, Pacific Grove, California (© Sheila Haddad/Danita Delimont)

A Siberian chipmunk on Mount Taisetsu, Hokkaido, Japan (© Ida Toshiaki/Minden Pictures)

Kalbarri National Park, Australia (© AWL Images/Offset by Shutterstock)

Partly snow-covered slope in Val Cervara, an old-growth beech forest, in Abruzzo, Italy (© Bruno D'Amicis/Minden Pictures)

Mount Taranaki, Egmont National Park, North Island, New Zealand (© Francesco Vaninetti/plainpicture)

Oil lamps on the birth anniversary of Sikh founder Guru Nanak Dev (© REUTERS/Munish Sharma)

Nuestra Señora de la Hoz, an old monastery in the Duratón River gorge, Segovia, Castile and León, Spain (© Arco Images GmbH/Alamy)