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

Chéran River running through a gorge, Savoie, France (© Jean-Philippe Delobelle/Minden)

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

Loch Leum na Luirginn and Loch Cleat seen from the Quiraing, Isle of Skye, Scotland, UK (© Sebastian Wasek/Sime/eStock Photo)

Albarracín, Spain (© Domingo Leiva/Getty Images)

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

Bison in Grand Teton National Park, Wyoming (© Brian Evans/Getty Images)

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

Vineyards of Barolo, Piedmont, Italy (© Marco Arduino/eStock Photo)

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

Chestnuts inside their burs (© Kai Keisuke/Shutterstock)

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

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

Iberian ibex herd, Sierra de Gredos, Ávila, Castile and León, Spain (© Juan Carlos Munoz/Minden Pictures)

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

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

Hokkaido, Japan (© Hiroshi Yokoyama/eStock Photo)

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

Chestnut-mandibled toucan nesting in the cavity of a tree, Costa Rica (© Greg Basco/Minden Pictures)

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

Autumn leaves frozen in Price Lake, Julian Price Memorial Park, Blue Ridge Parkway, North Carolina (© Richard Bernabe/Offset by Shutterstock)

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

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

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

A grove of American elm trees at Central Park's Mall, New York City (© AWL Images/Danita Delimont)

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

Kayaking in Glacier National Park, Montana (© Makayla Crist/Cavan)

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

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

Eilean Donan Castle in Scotland (© CBW/Alamy)