Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)

A tour group wanders through block 7 of Eastern State Penitentiary in Philadelphia, Pennsylvania April 30, 2014. Opened in 1829, with the original corrective system of “confinement in solitude with labor”, the penitentiary housed about 75,000 inmates in its 142 years of operation. At Eastern State reunions, former inmates, staff and guard gather to share memories and trade stories and get a chance to describe their experiences in question-and-answer sessions with the public. (Photo by Mark Makela/Reuters)

Touching and dramatic portraits and landscape shots have won prizes at Australia's prestigious photography prize. Photo: Winner of the NSW (New South Wales) prize: Peter Solness said: “I wanted to re-imagine the lost waterways, so I got my light-painting tools to work. In this image, water is being released from the top of the historic Centennial Park No. 2 Reservoir, which was built in 1925 and holds 90 megalitres of water. After 89 years of incarceration these waters now run free!”. (Photo by Peter Solness/Head On)

For 20 years, Joann Biondi worked as a freelance writer. Then one day she adopted a kitten that had been tossed in a garbage can and left for dead. That kitten had an unusual quirk; he liked to wear clothes and pose for the camera. So Joann started shooting, and then she got serious about photography. Fast forward four years and that kitten is now Lorenzo the Cat, a feline art photography project that has gotten both the cat and the photographer a lot of attention; gallery shows, museum exhibits, and stories in major media outlets throughout the world. Amid it all Lorenzo has remained a mellow dude who still likes to roll around in the dirt, chase lizards, and knock things off the kitchen counter when his food bowl is empty.

An employee of Paris city Hall removes padlocks clipped by lovers on the fence of the Pont des Arts over the River Seine in Paris, December 9, 2014. For years, visiting couples have hung brass padlocks on the iron grills lining the city's bridges to symbolise their undying love – they write their names on the locks, then toss the key into the Seine below. About 700,000 love locks are added every few months and Paris officials say they are damaging the bridges and threatening safety because of the added weight. (Photo by Philippe Wojazer/Reuters)

These snaps capture true winter wonderlands – as Mother Nature's icy grip takes hold of America's National Parks. From snow-capped mountains in Yosemite to an icy still Glacier Bay, the incredible images show their beauty is year round. In other breath-taking shots crisp frost lines the paths through Great Smokey Mountains and Crater Lake has had more than a dusting of snow. Here: Apostle Island National Lakeshore Park in Wisconsin. (Photo by U.S. Department of the Interior/Cater News)

A reveler and a child street vendor pose for a photo during the Banda de Ipanema Carnival parade in Rio de Janeiro, Brazil, Saturday, January 31, 2015. Rio's over-the-top Carnival is the highlight of the year for many local residents. Hundreds of thousands of merrymakers are beginning to take to the streets in open-air “blocos” parties. (Photo by Silvia Izquierdo/AP Photo)

Caporal dancers perform during the carnival celebrations in Oruro, Bolivia, Saturday February 14, 2015. The Carnival of Oruro which is a religious festival dating back more than 2000 years in an ongoing pagan-catholic blend of religious practice in the region, and is one of UNESCO's Masterpieces of the Oral and Intangible Heritage of Humanity. (Photo by Juan Karita/AP Photo)