Polar bear mother with cubs in Wapusk National Park, Manitoba, Canada

Lamplugh Glacier in Glacier Bay National Park, Alaska

'Legacy' mural painted by Josh Sarantitis and Eric Okdeh within the Mural Arts Program in Philadelphia, Pennsylvania

Flowing river inside a glacier cave, Vatnajökull, Iceland

The cypress tunnel at Point Reyes National Seashore in California

Two Bactrian camels in Kazakhstan for Twosday

The Washington Monument seen from the Lincoln Memorial in Washington, DC

Humpback whales and dolphins, Hawaii

Mount Logan in Kluane National Park and Reserve, Yukon, Canada

Great tits on a branch during winter in France

Flamenco dancers outside Palma de Majorca, Spain

Beech woodland in hoarfrost, Cranborne Chase, Dorset, England

Red lanterns hanging on trees during the Lantern Festival in Chengdu, Sichuan, China

Heart-shaped island with sandy beach, offshore coral reef, Indian Ocean, Maldives

American bison in Yellowstone National Park, Wyoming

Darwin's Arch with Darwin Island in background, Galápagos, Ecuador

'Go' by Kehinde Wiley, displayed inside Moynihan Train Hall at New York City's Penn Station

The Old City of Bern, Switzerland

The Ceremony Hall of Icehotel in Jukkasjarvi, Sweden

Rock art near Santa Fe, New Mexico