Medieval Aqueduct, Perugia, Italy (© Marco Saracco/Getty Images)

Mount Sneffels in the San Juan Mountains near Ridgway, Colorado, United States (© lightphoto/Getty Images)

Horseshoe Falls illuminated at night in Niagara Falls, Ontario, Canada (© Jianmei Wang/Getty Images)

Ammonite fossils from the Jurassic Period (© J Nemchinova/Getty Images)

Plitvice Lakes National Park, Croatia (© Jan Wlodarczyk/Alamy)

Mumbles Pier, Swansea, Wales (© Helen Hotson/Shutterstock)

Glade Creek Grist Mill, Babcock State Park, West Virginia, United States (© dszc/Getty Images)

Double-crested cormorants over Monterey Bay, California, United States (© Hiroya Minakuchi/Minden Pictures)

View of the Sanguinaires Islands from Corsica, France (© Francesco Riccardo Iacomino/Getty Images)

Octopus in defensive posture, Mayotte, Indian Ocean (© Gabriel Barathieu/Minden Pictures)

Moss-covered rocks in Puzzlewood, Forest of Dean, Gloucestershire, England (© Fulcanelli_AOS/Getty Images)

Danxia landform, Zhangye National Geopark, Gansu, China (© Weiquan Lin/Getty Images)

Adélie penguins, Antarctica (© Otto Plantema/Minden Pictures)

Château de Castelnaud overlooking the river Dordogne, France (© garethkirklandphotogrphy/Getty Images)

Brown bear in Silver Salmon Creek, Lake Clark National Park and Preserve, Alaska, United States (© Danny Green/Nature Picture Library)

Chattooga River in the Appalachian Mountains, North Carolina, United States (© mtilghma/Getty Images)

Sunset from Olmsted Point, Yosemite National Park, California, United States (© Robb Hirsch/Tandem Stills + Motion)